First off - I'm now one of ten horde characters on my realm with the title "Of the Nightfall". It's still a very easy fight for a Sarth tank, but having the FR set and good survivability after things go nuts made it easier. We did it with 2 1/2 healers (an elemental shaman started healing during the Vesperon phase) and all casters. And basically, the first time we killed Shadron with everyone alive it was a win. All credit goes to the other healers, tanks and DPS on the fight. I had the easy job, and I appreciate being carried. :)
Second - the change to improved mark of the wild does appear to give you and you only 2% more stats. So...only about an 8% nerf to health and a gain of 2% more agility. Yay?
I still think that druids aren't going to stop being tanks any time soon. Assuming that the changes on the PTR go live (10% stamina loss, 6k armor loss), the loss of stamina and the loss of armor are both survivable hits for tanking viability. That said, I also don't think that druids are going to be reasonably chosen for progression content where a single tank matters heavily unless there is some stupid gimmick that favors having 10-15k more health than another tanking class. With the current changes on the PTR, simply put, right now druids are outclassed by other tanking classes in every single category save one - health. And health is not as useful for progression as a lot of other factors, particularly when encounters are balanced around the lowest health values.
Of course, it's very early in the PTR and a lot can and will change by the time 3.1 is released, so relax a bit.
But this isn't about that. This is about how to fix druids in the long term. These are a couple of posts I made on the official tanking forums, and I figure that they should more likely be in a blog than there. Also, I wanted people's input on them; I may be missing a lot of ideas here too. Also note that as Greenkappa pointed out, none of these big changes can be done for all of WotLK. There's no way to radically revamp feral tanking right now. That'll have to wait for the next expansion. So this is more of a post-mortem along with some ideas on where things may have to go.
There's a few problems with bears that aren't easily solved. The first and probably the biggest is itemization. In BC bears had very specific sets of gear that were not easily replaced. This meant that if you didn't get lucky with one drop, you would be significantly disadvantaged. It also meant raids were not the primary source of gear upgrades; heroics were via badges. It meant that druid power levels could be balanced reasonably via itemization (since they only had one very flawed set) but that they had very bad feelings about said itemization. And even then, the power of gems, enchants, and using jewelry that was designed for other classes meant that druids scaled too well compared to other tanks. It also had the weird side effect of making PvP gear awesome because of specific requirements to uncrittability that didn't care about things like block or parry; it was too easy to use resilience over defense simply because a loss of defense wasn't expensive enough.
Then we get to WotLK, and we have a totally different problem. Itemization is easy because so much of the itemization 'needs' gets covered with talents. Innate dodge, uncrittability and no real stat requirements. This (as Guaritor has pointed out) leads to really weird scaling issues, where a druid can have a range of 20,000 HP difference between one and another, or 20% more avoidance than another. Furthermore, because there is no extra armor gained from gear, we have the weird situation where anything really can be used without penalty. Spellpower leather? It's got stamina and crit and as much armor as the next piece does. DPS jewelry? Sure, it's got agi and stam on it. This has another side effect of allowing druids to tank reasonably well while wearing nothing but DPS gear, a side effect that almost guarantees druids will be doing DPS instead of tanking on any encounter where tanks are interchangeable and not as required (especially if you need to tank only part of the time in a fight).
No other class has this kind of variability in gearing with the same tier of gear available to them.
Of the two situations, one was balanced via poor itemization, one was simply not balanced. Both stem from the same issue: bears scale too well around too few stats. In BC it was armor and avoidance stats. In WotLK it is stamina and to a lesser extent agility.
Simply tweaking things here and there isn't going to solve the issue that druids can get 20k differences in health; that number is only going to increase with the advent of epic gems and better gear. Requiring druids to have some level of some stat found on DPS gear might help some, but only for a bit; once it becomes trivial to meet that level via improving ilvl gear, you'll run into silly scaling again.
So what are the problems that druids actually need to solve?
Bears need to be uncrittable.
Bears need to have a way to use leather melee DPS gear as tanking gear or have their own set of gear that is balanced for them. If they use melee DPS gear, it means more options but more balancing headaches. If they use tanking leather, it means fewer options, harder gearing choices and potentially wasted gear drops.
Bears need a way to innately balance tanking jewelry that is balanced around plate wearers.
Bears need a way to innately balance gems and enchants that are balanced around plate wearers.
Bears need to make up the stamina loss on leather DPS compared to plate wearers.
Bears need to make up the armor loss on leather DPS gear compared to plate wearers.
Bears need a mechanic to balance a lack of a shield.
Bears need to scale with this gear in such a way that they cannot stack one stat over all others.
Bear talent specs need to distinguish themselves from cat talent specs in such a way that one says 'I'm a bear' - which is difficult since feral talents are all in the same tree.
These are hard problems to solve. No other class in the game remotely has these kinds of issues with balance. The closest analogy is the holy paladin, who has their own loot table and shares jewelry that is close enough to itemization that they want that it doesn't matter. And honestly, at this point that might be cleaner. If you assume that druids are going to use tanking jewelry, gems and enchants AND they can get their own gear sets, you can balance most of that easily as well as make requirements on that gear such that they can't drop it easily. For example, the Polar set wouldn't have been an issue in TBC because it had no extra armor whatsoever.
Making agility count even more doesn't fix all the issues. It fixes the polar set - perhaps - but druids already get tons and tons of agility all over the place. In my polar set I still have about 500 agility. If we made it analogous to defense rating for plate wearers, that's only 189 agility to go. That's not that hard at all. And it causes another problem; reliance on raid buffs. Horn of winter would provide 150 of that agility, for instance - does that make much sense?
If you did do this, you'd have to make tanking leather. Otherwise, it doesn't do enough to make DPS leather valuable for druids, and then we get into the same situation as before where bears go for PvP gear and random crap things like the Polar set just because they can.
The core problem I believe is still that druids can choose to use things like the Polar set and that they have too high a scaling factor with stamina. The recent HotW nerf does nothing to fix either of these things especially.
I still think that tanking leather is likely the way to go here. Remove the uncrittable benefit from SotF and bring back tanking leather all over the place with defense on it. Make defense a desirable stat by converting parry to miss and dodge, and make defense the best avoidance stat for bears over agility so that they actually want the defense on the gear they get. Make 4 sets of tier gear, allow a lot of craftable gear and some kind of turnin tokens for rogue gear to turn it into feral tanking gear. Have cats and rogues itemized the same and have bears need armor and defense on their leather to remain competitive. Balance their stamina multipliers around the idea that bears will be going for tanking jewelry and values. Make SD more valuable and make strength a more desirable stat for bears. Give lots of early craftable gear choices and quest drops.
I don't like this idea so much because it does eat up more item slots on tables and may result in wasted gear, but that's probably the easiest way to balance the spec.
Barring that... I don't know. If you don't do it that way, you need to make dps gear so valuable for bears and so needed for bears that they won't think of taking anything else. Possibly taking the crit chance and turning it into anti-crit? (and not agility - just crit rating). But that feels kludgy. Making AP be armor or stamina, haste into dodge...all of these things have been mentioned, but unless druids are forced to use dps leather over things like the polar set they simply won't be balanceable.
And all of this can't be done any time soon. The best suggestion I've seen so far involves having diminishing returns on health gains from stamina, giving druids more cooldown options to bring them in line with recent warrior buffs and baseline DKs, and nerfing their current health and armor to what they are on the PTR. That's probably reasonable, though I'd recommend keeping the current multiplier on HotW but having DR on health. That should solve the problem significantly without hurting more balanced bears. Barring that, possibly just nerfing the Polar set would help tremendously. Or making it so that only stamina on gear is multiplied so heavily by various buffs and stats and dire bear form, similar to how armor works now.
It is frustrating though, in that a lot of these issues were brought up by myself and others during the beta but nothing really was done.