I think the trouble is, this could end up just like how Cata dungeons got nerfed to be like WotLK dungeons. All those players who are simply bad will, come the expansion, end up whining on forums that they can't play any more because it's too 'hard', and Bliz could end up just screwing it up all over again.
Bliz are just shitty developers. A good developer does what's called iteration. They take what they have and develop it, making subtle changes over time to improve on it. Blizzard just repeatedly scrap what's broken, sometimes years after they made it and with no iteration at all, only to replace it with something equally broken, that also will not get any iteration (see abilities and talent trees for a fine example).
They made huge changes to how the launcher works, which should allow them to make patches to the game on a week by week basis. They could have fixed the massive class balance problems before endgame very simply, by shifting the levels at which classes get abilities, or by buffing certain abilities only at higher levels, through talents, or the passive abilities classes get at higher levels.
Instead they left the game an unbalanced mess since they first fucked it up with Cata. Why anyone should believe they intend to fix anything in MoP is beyond me, when their history on the issue right up to the present, points at them saying (not doing) just enough of the right thing to keep people paying (and buying MoP), then carying on as usual once everyone has forked out for the expansion (compare that to how fast they fix issues with endgame raids, with patches for those coming out sometimes next day after the issue is raised, even if hardly anyone is doing that content yet).
I'm not going to be paying up until I see not only balance at the point MoP is released, but a commitment to improve upon that balance in the 5.1 and 5.2 patches (and even then chances are I'll just be paying to play some other game from a better developer anyway).
