This really looks slick. I have no idea on pricing, but the idea of half-width multi-processor motherboards sounds very promising.
http://www.supermicro.com/products/nfo/1UTwin.cfm?gclid=CN_dvJz_1qACFQwNDQod3hJJxw
http://www.supermicro.com/products/nfo/1UTwin.cfm?gclid=CN_dvJz_1qACFQwNDQod3hJJxw