I suspect it will depend a lot on what sort of active survival abilities tanks end up with.
I mostly agree with Blizzard's comments that threat isn't really a central part of encounters anymore. Firelands especially. I do think that there is room for threat to be a valid part of the game for tanks, but it usually fits in only when a portion of a fight is tank-and-spank on a newly pulled mob. Those are becoming a rarity.
It will fix the really undergeared tank part of things. It will fix the annoying "our tank can't threat properly, so I as dps have to just stand around for a bit every now and then. great fun, that" occasions. I think it might lead to more tanks in the LFD thing, though not by as much as people are hoping... the main reason, IMO, people avoid tanking is that tanks are given the leader role in dungeons, being the person who sets the pace in nearly every single group out there. Plus I hate tanking heroics in case I have to AFK! Much easier to AFK for 60 seconds as a dps who no one misses. Tank AFKing shuts down the whole group often enough... but I digress. :p
All of these potential benefits can wind up not mattering all that much if tanks don't really have much to actively do, though. Something beyond the mechanics of each individual fight (which IMO still will be the biggest parts to playing, I think) to separate the good tanks from the barely capable tanks. You could argue that threat didn't do that anyway, and you'd probably be right... but they have an opportunity here to make an improvement. We shall see how that works out.
This whole transmogrify thing is something I'm a whole lot more disappointed in, though! I may be admittedly in a minority here, however, but... grar. I saw what armor dyes did to EQ, effectively killing the ability to tell anything about anyone based on their armor overnight. It's not that I"m being all judgmental about people, but it's... meh. Never liked it. We'll see if people ever stop looking the same after that gets added into game. How long will we see all Paladins wearing T2 or T6, for example... Ah well. As a Druid I can support this after a fashion since it comes part and parcel with this soul void bank thing which lets you keep 100 (or more?) pieces of gear in. I have kept just about every weapon I've owned since Burning Crusade, not to mention all visible pieces of T7 on up, and every Druid shoulderpiece from all raids (except old Naxx!
) and even a dungeon set or two. So. I will finally have bank room again. Hooray!
I knew I shouldn't have just vendored the T8 Rogue lookalike shoulders and hat just the other day, though!