While Reesi and Tangedyn (note: no guarantees they'll stay in their feral spec/gear) did an awesome job about what to do for the spec and glyphs for a hybrid build, I didn't see a lot on the gear. And...I still don't. Probably because it's a lot harder to evaluate.
Also a note on the glyphs: don't be afraid to take a stack of disappearing dust and swap glyphs as needed. You should be doing this on a case-by-case basis anyway. If you don't use feral faerie fire, the glyph for it is not great. If you're not hitting multiple mobs, why take maul? The prime glyphs are almost always going to stay the same for any fights that have you using hybridity, but if you're just tanking swap them out!
For this I'll give two choices: max DPS and max survival. The Max DPS will give some credit to survival (and vice versa) but ultimately what you need is up to your role; if you're primarily DPSing with occasional tanking light stuff max DPS should be fine. If you're tanking all the time you'll likely have to go with maximum survival.
Gear choices:
The best stat for a hybrid set is agility. Everything should have it. That's true for DPS or survival. The second 'hybrid' stat is mastery. This is the best secondary stat for cats and the second-best for bears. So far, not a lot changes, though your gemming priorities may change somewhat (favoring agility gems over anything else and disfavoring stamina over agility/hit gems).
For max DPS go mastery above everything else. For reforging, the primary reforging target should be mastery if the gear doesn't have mastery. The second one should be expertise (if below the dodge cap), then crit, then hit. Why? If you're planning on being a bear expertise is going to benefit you from a threat perspective and from a savage defense uptime perspective more than crit or hit as long as you're below the dodge cap. After that crit and hit are fairly similar. As has been shown recently, going hit/expertise/crit/haste/mastery is really a matter of choice more than massive changes in overall DPS value for a cat.
For survival, the best secondary stat is dodge. Reforge the highest non-mastery stat to dodge whenever you can, favoring haste, then hit, crit, expertise in that order.
Avoid tanking rings, necks and cloaks. They'll be basically horrible for dps and do not give enough survival gains to warrant their value unless they're significantly higher ilvl (2 tiers) more than what you have.
Tier pieces:
On Tier pieces: the 4 piece for cat is very, very strong when going cat 100% of the time. The problem is that whenever you switch out of cat the buff disappears completely. That means that on any fight where you're switching back and forth every 30 seconds the buff is just going to not be worth it; using 3 GCDs to mangle just to have the buff for 30 seconds isn't going to be as good as having suboptimal stats for bear or cat.The 4p is pretty nice for bears too, but the actual pieces really vary, and for hybrids (especially ones caring about survival primarily) the biggest importance is ilvl over basically anything else. If you have the choice of getting a heroic non-tier piece to replace the nonheroic tier piece - for a bear, this is a good choice. For a cat it's a harder choice but likely the right one.
Note that the 2p for cats is just perfect in this setup as the rake will keep on ticking while in bear form. Yay threat!
In terms of what nontier piece or pieces you should have, it depends. For non-heroic content, Tsanga's helm is the best. It is the only helm with mastery. The tier helm has hit and crit, the offset from Cho'Gall has haste and expertise (ugh). A second choice is the Poison Protocol shoulders, which also have mastery. The Double Attack Handguards are also not bad compared to tier; at least they don't have haste.
For heroic, the best bet is the Sark of the Unwatched, which has crit and mastery vs. haste and expertise.
The best tier piece is the legs, which have crit and mastery and nothing is better at either level. Then the head, then maybe the chest due to the socket bonus being better. In a perfect world I'd go for (non heroic) Tsanga's helm, Double attack handguards and purchasing Morrie's and then going for tier legs and shoulders. For folks getting most of their gear via valor points by necessity you'll likely pick up the tier chest; buy a helm and then work on shoulders and buy Liar's handgrips. For heroic mode go for tier legs and helm, then Double Attack handguards, Sark and Poison Protocol shoulders.
Trinkets are interesting. Ideally you will swap trinkets as needed for certain fights and use others for others, but there are some 'much more better' ones than others here and there.
Max DPS:
- Fluid Death has high agility and a reforgeable hit to mastery. Good stuff.
- Essence of the Cyclone has the raw agility but the proc is almost completely useless for bears.
- Unheeded Warning has lower agi than many of the choices here and has a proc that is completely useless for bear survival (it doesn't even affect SD). Still, it's one of the highest DPS trinkets that exist.
- Tia's Grace is almost as good as Fluid Death for cats and actually a bit stronger for bears on most non-Heroic Nef fights due to the extra mastery. (But don't use it for Nef tanking!)
- Quicksilver Talisman has tons of agi and reforgeable crit. The potion part isn't particularly useful but it's a good alternative for a second trinket.
- Prestor's Talisman also has high agility but has a meh proc for bears.
- DM: Hurricane is similar but even more useless to bears.
Max survivability:
- Fluid Death has high agility and a reforgeable hit to mastery. It's likely the best hybrid trinket.
- Tia's Grace is almost as good as Fluid Death for cats and actually a bit stronger for bears on most non-Heroic Nef fights due to the extra mastery. While Fluid Death has more overall agility the mastery can overtake it, especially when taking smaller hits. (thanks, Nica!)
- Mirror of Broken Images only has a survival proc, but that it is mastery as the main stat helps both specs and the actual on use ability is amazing for this tier's raiding content.
- Vial of Stolen Memories is horrible for DPS, but between the high stamina and the huge dodge use (which will be very high in an agi-centric gearout), it can be very good - especially on magic-heavy fights.
- Symbiotic Worm is a good but not great stamina trinket; use it if you don't have the vial or need a ton of stam for some reason.
- Quicksilver Talisman has tons of agi and reforgeable crit. The potion part isn't particularly useful but it's a good alternative for a second trinket.
- Prestor's Talisman also has high agility but has a meh proc for bears.
- Bedrock Talisman is good for survival but completely useless for DPS.
- Essence of the Cyclone has the raw agility but the proc is almost completely useless for bears.
- Unheeded Warning has lower agi than many of the choices here and has a proc that is completely useless for bear survival (it doesn't even affect SD). Still, it's one of the highest DPS trinkets that exist.
- DM: Hurricane is similar but even more useless to bears.
For me personally the choice is clear - Fluid Death is a win for both specs. An alchemist is probably in luck too. After that the generic one would be something like Unheeded warning or Prestor's talisman depending on what you have. For harder fights swap to a stam trinket + mirror of broken images. Trinkets are the easiest, best way to customize your gear on a fight-by-fight basis, so really do collect them all.
Enchants:
Head:
Max DPS: Arcanum of the Ramkahen
Max Survival: Arcanum of the Ramkahen or Arcanum of the Earthen Ring
While 90 stamina is quite hefty you may be fine with the stamina you have - in which case the 60 agi beats 35 dodge rating any day. The haste is useless for bears, but it's okay for cats. Note that this is a very good place to get a ton of stamina cheaply, so consider doing so if you need more health.
Shoulder:
Max Survival: Greater Inscription of Shattered Crystal
While the Unbreakable Quartz enchant is solid, getting both agility and mastery makes up on the hybrid side compared to both. Again, if you need the stamina go with stamina - but otherwise this is a good place to compromise in favor of DPS and avoidance.
Chest:
Max DPS/Max Survival: Peerless Stats
No real debate here. The stamina is nice but this gives enough overall value that it's worth it.
Legs:
Max DPS: charscale leg armor/dragonscale leg armor
Max survival: charscale leg armor
Okay, so technically the dragonscale leg armor wins for DPS - but it's much closer than you think. 55 agility gives 110 AP as well as crit; based on weighings right now that's about 85 EAP vs 55 EAP, which is way smaller. So is 30 EAP worth 145 stam? In most cases you're not going to be able to find a better tradeoff than that. So I'd recommend in either case to go with the charscale legs.
Feet:
Max DPS: Major Agility
Max Survival: Assassin's step
If you can afford it I'd go with assassin's step in either case, but technically major agility is better for cats since they gain nothing from the movement speed increase while in cat form. Lavawalker is also a good choice for a hybrid that favors a bear.
Wrist:
Max DPS/Max Survival: Enchant Bracer Agility
Easy choice here. For leatherworkers it's a bit more tempting to go for the stamina enhancement,but I'd recommend going for the superior agility there as well.
Gloves:
Max DPS: greater mastery
Max Survival: Glove reinforcements (old world)
Yes, the glove reinforcements are still just that good for bears. Sigh. The mastery enchant isn't too bad though.
Cloak:
Max DPS: Greater Agility (old world)
Max survival: protection
For this I'd recommend having two cloaks if you can or going max survival here; the old world enchant is not super strong (22 agi isn't huge) and 250 armor is quite good for bears (it's worth about 40-50 agi for bear survival depending on the fight).
Weapon:
Max DPS/Max survival: Mighty Agility
Fortunately this is an easy choice.
Gems:
The primary goals for both specs is getting agility whenever possible. Where things differ is mostly in which hybrid gems you use and which sockets you go for.
For max DPS go for these choices:
Red: Delicate (agi)
Yellow: Adept (agility/mastery)
Blue: Glinting (agi/hit)
For max survival, go with these:
Blue: Shifting (agi/stam)
Then we get to the metagems. And that's a problem. The metagem for DPS is at least a 3% dps gain overall; no single item or enchant or gem comes remotely close to how good it is. The metagem for tanking, however, boosts the one thing that bears are great at - armor. While that's a clear sacrifice, the second sacrifice is that the tanking gem also requires having multiple yellow gems, which are also a somewhat contentious choice. Ultimately what you choose is going to have a big effect, and since helms are hard to come by this may be really tough. Since I think that the hybrid build is about tanking first, DPS second I'd likely go with the austere - but either is a reasonable choice. Just make sure you understand what you're choosing.