I see a lot of people here worrying about suboptimal specs and what-not, but I honestly don't think it's going to be a big issue in Classic.
One thing I'm looking forward to is since it is a finite game, meaning there will eventually be no progression, people will care less and less about whether someone is super, number-crunched, optimal spec to bring to a raid because 1)Most people will eventually out-gear the raids and just continue running them for the rep, off-spec pieces, or that one item they missed, and 2)People will eventually know the mechanics of every boss fight like the back of their hands, so they can do them with sub-optimal specs and gear.
Sure, at the start, when everyone is trying to rush through the content first and gear up, they will want only the optimal specs, but eventually Boomkins, Shadowpriests, Bear tanks, Pally tanks, cat dps, BM hunters, ret dps, arms dps, etc doing all this stuff.
Eventually the pressure to be at break-neck progression level will be gone entirely. People will be able to play the game how Blizzard probably originally planned it to be played.