There is also the possibility apple could quad line up the mac pro. run 4, 6, 8 and 12 core models. imagine the fun they could have on pricing that lot.
Yes, it is possible, but not likely IMO. This is why:
1. Apple is a company which very well understands the costs of complexity.
2. A quad iMac and a continued quad PM create overlapping product lines with internal canibalization.