Something that I was hoping Blizzard would do, and didn't, is change how Destro played with the deeper talents. That is to say, Affliction has Haunt which becomes their new top priority, Demo has Demonic Pact and a strong DPS cooldown which can change some stat prioritization or at least where your DPS is coming from (the casters you're benefiting), yet Destro only gets a non-primary nuke that comes in at a lower priority than several of their other spells. I dunno, it felt meh to me in 3.0 and it feels meh now. 40/31 feels like more of a Destro spec than Destro to me. It has a new mechanic that's fire based (SF execute), strong fire synergy which was supposed to be the hallmark of Destro, and Imp synergy, another supposed Destro hallmark. So while it's technically a hybrid spec, I feel that it represents the spirit of the pure Destro spec better than pure Destro.
Just this man's opinion, but I actually look forward to playing it.