It depends on your perspective I guess. From an academic stand point you will just see more of other powerful builds. As already mentioned the incantrix and dweomerkeeper would get a boost in play, along with arcane thesis, easy metamagic, and practical metamagic (more kobolds, like we needed a reason for more kobolds) for metamagic focused builds. Quite a few of the ex cleric builds would transition over into druids with planar shepord to allow fast casting. There would also be more warweaver builds for whole party buffing on the fly. Clerics also would end up with alot more feats to select. And on the whole, magic would shift from buffing to more blasting builds for those that don't want to try to optimize the nerfed buffing.
As for turn undead, it would not get used. The problem with using turn attempts to actually turn stuff is that hardly any PrC's advance your ability to turn. Also as you move into higher levels, +1 CR is not 1 or 2 HD usually, so you cannot turn anything anyway without heavy optimization. So I would suspect domain devotion feats might pick up some of the slack in feat selection, but not much.
If on the other hand this is a DM nerf to bring things under control, it will only lead to greater frustration. Something else will pop up on the DM radar that he will not like, just after he thought he got everything fixed. I have seen this happen and it just leads to a long list of DM nerfs and frustrated players that keep having to alter their characters. It is fine if each new game brings an additional nerf, but tough if instituted mid game (especially when it happens more than once).