I agree with the idea, but Apple is stuck with Intel's Xeon roadmap, which at this point multi-processor is lagging far behind the single processor lines.
Although Intel's Westermere-EX was last updated in late 2011, the specs are still pretty good. Those CPUs have up to 10 physical cores (20 virtual thanks to hyperthreading) and 30MB of L3 cache. The clock speed isn't amazing, but that's to be expected when you have to deal with the heat from 2.5 billion transistors.
The Ivy Bridge version is supposed to ship in Q4. It should have even better performance.
I think we should also look up the exact details of how "stuck" they are with Intel, if this new-Mac-Pro-like-thing ends up being as revolutionary as some hope...I seem to recall way back at the "switch" to x86 that there was some deal with Intel and Apple that only locked them together for a certain number of years? That number of years may be approaching, I don't remember the details.
