Allow us to set the center of mass for objects and allow for objects to be affect by this. This allows for better arrows and throwables.
I think what you really want is being able to set the center of force. By definition, when the COF = COM then linear force does not impart angular velocity. When COF != COM, some percentage of linear force gets converted into angular velocity. That is how PhysX works. I would hope Bullet has a similar construct.
Yes, that basically.
Bullet does support this. It either works right now (which you could test) or we can put in a bug.
Create a mesh ball and move the origin to some other location
Upload ball and move the registration point. (i Just tested this and it kind of works)