nate066 We won't have colliders in 4.2 but we're not counting it out for the future. I can say that we don't want to build an extensive physics system. That would be fun, but it's difficult and we already have lots of animation tools to build! Our physics systems aren't intended to be used for an entire game, just to give dynamics for your animations without using a lot of CPU. That said we do want to have a way to bridge the gap between animation physics and game world physics. Often that can be done by moving or following a bone. Collisions are harder. Circle bounding boxes could be a first step, as you mentioned.
Getting ahead of myself, we have plans for mesh physics after 4.2. That is where a mesh reacts to bone movement using physics. We have a prototype for that, here's an example:
Only the bones are animated. The fish image is the mesh and bends in the simple way you'd expect. The wireframe is the mesh with mesh physics applied. It's somewhat subtle in this example, but you can see the dynamic movement in the mesh. All that movement comes from the simple bone animation and didn't need to be animated by hand! You will also be able to have some of the mesh's bones move from the mesh physics, giving you enormous power.
It's super cool, but it does use a lot of CPU. We usually try to make things very efficient but some features like clipping or mesh physics require more processing and care needs to be taken with how they are used. In comparison, the physics in 4.2 are relatively cheap and don't use much CPU.
Anyway, we continue to work on 4.2 every day. I know the wait sucks. We want to get it released as much as you want to use it, but it has to meet some minimum requirements first. Even when it feels like we're so very close, it takes a lot of time to iron out all the details, even for a beta release.