The wiki for the 2013 MacPro seems to indicate that it could support a 12 core Xeon, which would allow for 24 physical cores. However, the way it was written was somewhat ambiguous. Also, considering that 10 core Xeons are just coming out for the general public, it seems unlikely that 12 core Xeons will be available anytime soon for those who aren't associated with government agencies or mongo tech companies.
I am both intrigued and suspicious of that thermal core in the cigarette disposal can/I mean the new MacPro. In theory it sounds brilliant. I just wonder how well it will soak up heat. Also, the single fan design seems inadequate for cooling the amount of heat generated by dual GPU's, dual CPU's, etc etc. But I will be happily be wrong. It would be nice not having to worry about six million heatsinks.