What is there is essentially a prototype. It works, but will change significantly.
The biggest part of physics is the editor supporting non-determinism. You can have the physics reset from frame zero, so on frame X the pose is consistent. Or you can have physics applied continuously, so on frame X the pose depends on whatever was happening previously (in the editor, not from the animation). The same is true at runtime: users will want to control when physics gets reset or forward to a particular time (which can be expensive). Usually it's applied continuously but you may want to reset when making big changes, like resetting to the setup pose, so the physics controlled parts don't bounce around wildly.