I'm going to make a wild, wild guess. Apple decides to simplify model lines and parts supply by basing the new MP on the iMac. Low-end starts with a standard, single CPU i7 iMac. Then introduce a special, higher-end iMac with two (or more?) CPU's. Maybe with a special cooling system? The iMac is partnered with a combo drive/expansion-box tower using one, maybe even two, Thunderbolt ports. Voilà! iMac Pro. Thoughts?