@AdamOwen...
I have multiple (composite) collider support in the pipeline and got very far along with the interface and such, and it would probably be fairly straightforward to complete it. The catch was (there's always a catch), I had to make it work with frame based animation, and that's why it isn't built in right now.
Uni2D does look really really awesome, and I can see getting it myself for some quick prototyping physics based games. I personally prefer explicit control when building on constrained platforms
About automatic polygon collider generation - I had convex shapes working at some point on a branch somewhere, but I don't think I'll complete/integrate it anytime soon - theres still a lot more to do, and Uni2D looks like it'll just do it automatically. The colliders will be directly compatible, so you should be able to mix and match
I'm really itching to get on integrating support for the Farseer Physics port... that could be really really awesome (imho). Box2D is so much more stable than Physx for 2D stuff. Maybe after 1.80, if there is any interest.