I think that adding a 4th axis to the current MPCNC would be more useful. Not only could you coax the design to create and size round parts, but you can also add non-round features to them (think gear teeth), you get orientation control, and you dont have to worry about workpieces flying off and killing you.
Cycle times would be a little longer, but implementation would be easier, and the resulting machine would be safer and in some cases, MORE capable.