Why now? Seriously they might as well just wait a few months more until Ivy-Bridge EX processors are out, with the possible inclusion of a dual 8-10 core, 16-20 hyper threaded cores...using Sandy-Bridge EX processors would be outdated.
Xeon processors are always behind in terms of adapting new architecture. I'm sure based on the new redesign, switching to Ivy Bridge Xeon would be a breeze.