It's Ricoh finding a new audience for their modular camera system. You get the quality and engineering of Ricoh's body and interface design, which is the absolute best in the mirrorless market, and you get to use that with M-mount lenses. Plus, the module lets you save customized lens-correction settings for multiple lenses.
When the NEX-7 comes out, then we can talk (OLED EVF, microlenses in the sensor).
Also, have you read the early information about Nikon's EVIL system? With a crop factor like that (2.5 or so), using Nikkors on it would be sort of ridiculous.