Many options have emerged for shooting Leica M and Zeiss ZM and Voigtlander for M lenses: Fuji X-Pro1, Sony NEX, Richoh GXR, Olymps OM-D E-M5, Panasonic 4/3, etc. I have extensive coverage on SONY NEX as to performance in my Guide to Leica.
To date, there does not exist a full-frame camera accepting M-mount lenses (with or without an adapter), other than the Leica M9 and Leica M monochrome from Leica. Even a 1.2X or 1.1X sensor would be quite interesting.
There are ray angle issues with M-mount lenses, especially on full-frame, and perhaps this is a difficult problem. But it seems to me that a vendor could “clean up” as long as Leica wants $7K or 8K for a camera body— by offering a $3K or $4K alternative, complete with Live View and sensor and firmware that compensate for ray angle issues.
And not just a color, but a monochrome version also. Shooters with Leica M lenses are by definition not very price sensitive as a group, but even they draw the line at $8K for a body.