Hi William,
With multiple SSDs and cheaply available RAM I find the only thing holding back mega VSL sessions is CPU. Now if the new MacPro is handling 4k video like a high end PC handles HD then it's sort of giving 4 times the performance. This could equate to about 400 instances of VI-Pro.
http://www.fcp.co/final-cut-pro/articles/1307-the-first-24-hours-with-apple-s-new-mac-pro-and-final-cut-pro-10-1
Now if this can be translated into audio then having everything on one machine will be much more elegant, timesaving and powerful. Just have to see how the software evolves.
Julian