I know a lot of people talk about if they will still be able to tank or do enough damage but those are just numbers, which can easily be adjusted if they should not fit. I am more troubled about basic game mechanics.
Right now my biggest concern is how the new equipment, talent tree and stat conversions will kill the hybrid feral, which imho always was the reason a feral druid (especially kitty) found a spot in a raid (and was fun to play btw). Even if feral cat druids would do same dps as rogues, e shamis or even off warriors i would never ever take one over a rogue or e shami if they were not able to offtank and squeeze out some emergency heals once in a while.
One of the main reasons to bring melee dps instead of ranged is for their interrupting qualities and kick, pumel and wind shock are all very reliable at doing that, even the new improved maim is not. To interrupt something as a kitty you have to have at least one combo point, 35 energy and no global cooldown, a rogue in this situation only has to have 25 energy. Just one example where pure kitty support is either completely lacking or just subpar compared to rogue/off warri/e shami (always forget that paladins are considered to have a dps tree now too, i know they have lots of support, just don't know if they can interrupt on short cd).
In BC this was ok, our support came from flexibility. And i liked that approach, i don't want rogue toys like vanish, poisons, aoe attacks etc. I don't want to become just another rogue with an uglier skin. I liked to be subpar but borderline viable as kitty in terms of damage and making up for the gap with flexibility. And i fear in wotlk we will end up still beeing subpar (if not in damage then surely in utility and thats the worse part) but now without the flexibility we had before.
The main problems i have right now are a bloated feral talent tree, the equipment and ability conversion changes. There are now several heavy impact bear only and cat only talents and you hardly have enough talent points to skill one of them. But that is actually the part i have the least problems with. If we really turn out to be very competitive dmg and tanking wise i can easily sacrifice a few points here and there.
What bothers me most are the equipment and ability conversion changes. I know a lot of people are thrilled at the idea to tank in dps gear but actually that is what we always did, at least as much as we will do in wotlk. The only slots i swap for dps gear are trinkets, rings and cloak. All of those (maybe except the cloak) i will still swap in wotlk (trinkets and rings actually will be even more importaint to be swapped for tanking in wotlk).
Druid itemization was very good, especially because of the good ability conversions. And they were very hybrid friendly. Agi for example was a great stat for both bear avoidance and cat dps and we had it in loads on our gear. And while we will still have it in loads it just wont be very good anymore because of the nerf in conversions to dodge and crit. Strength on the other hand will still scale nice in both forms (though it only helps with threat as bear and not with avoidance), just it wont be found on our gear anymore. So while in BC i could get badge and Tx equip and socket it with agi to get an awesome bear and cat item now i have to get 2 badge or Tx items for the same slot, one socketed with crit rating, the other one with dodge rating.
Int won't be found on our equip anymore either. In wotlk i will loose more than half of my mana, and with tranq and rebirth beeing around 70% base mana and combat forms beeing 35% base mana i guess nurturing instincts has become a joke, even if you would have the talent points as hybrid to take it. The new imp lotp won't help much either i guess. 8% of nothing is still nothing. And it doesn't change the fact that you will have to change shape after a few casts to refill, loosing even more mana you first have to gain back.
But then again when druid tanks in full tank spec and druid cats in full dps spec turn out to be overpowered a hybrid druid might be just ok .