Multi-socket mobos and CPUs command a significant price premium. I, personally, when building a new system will probably just build a 6-core single socket system, rather than buy a two socket mobo that can take two quad-core processors. Maybe spend the money saved on more memory, faster hard drive, etc.

I suspect Xeons will remain socketed. As a side benefit, Intel probably won't mind if people spend extra money on principle to get a socketed processor.