Node-based UI for effects.
A node based environment, should be implemented esp for basic tasks like applying the same effect to multiple layers, alpha mattes, value parenting (like the current pick whip in the expression options), Anything that you can currently do using an adjustment layer (but would be selective), I'm sure many more uses. You could use it in tandem with the layer system, but would be an easy way to do these kind of tasks without copying and editing multiple instances of the same thing.
It would be nice... but Adobe are happy to not innovate. If they had to be innovative there's no way they could rush out a buggy version every year! Quality company