I have a fair bit of influence and clout over on unity forums so you can expect some sweet custom coming your way. But I can only recommend things I think are idiot proof (mostly because Unity is idiot proof up to a point). I feel spine is by far, coming along to be the best solution for pretty much any game including 2D sprite based affairs.
Why 2D sprite based games? well for a start you get a robust framework, but you also get the POWER to animate small anchor points, for example a hat, a sword and so on, as well as it handling a huge gamut of game engines.
I'd recommend you figure out a way to be able to insert different things "in between" or be able to offset layers a certain amount for true flexibility though, otherwise it becomes difficult trying to synch up a behind and in front animation for the same thing.
Other than that (I read you were already adding stronger cel based support plus events) I can't think of a single reason to use 2D toolkit or ex2D really. It pretty much covers all bases for 2D game development.
Loving it.
Last night had 8 characters on screen in Unity, with a single draw call (Spine plays nicely with dynamic batching). Animations blended between each other smoothly without even needing to bother with Mix, just SetAnimation and setting up tweens between in the skeleton asset. Really do enjoy using Spine. I only code with it though, Giuseppe, our creative lead is the man to use the editor, so he will be giving any feedback if needed.
Please keep up the excellent work, I know it's tiring but you're on the cusp of WORLD DOMINATION.
