I agree with Tom that I don't see the need for Ricoh to make a different mount module. M-pretty much covers it all.
Lenses you can adapt onto M mount (besides M, obviously):
[*]Leica Screw Mount LTM
[*]Contax G/ RF
[*]Olympus Pen F (no vignette)
i.e. Basically all the best lenses made for rangefinders and SLRs. I have ignored medium format (which is no certainly possible).
i.e. Less than stellar CCTV lenses and the proprietary CSC lenses (which is why I refuse to buy a full arsenal of M4/3 or NEX lenses), particularly lenses that require electronic extension and focusing. Some other lenses are borderline. e.g. Contax G is not normally compatible, but MSO do a conversion service.
I think the GXR A12 module is the possibly best mount available for legacy lenses.
[*]It can mount almost any M or LTM lens, including lenses not mountable in M4/3, NX, etc.
[*]It has a large sensor area, reducing crop factor. Better than M4/3, especially PQ, N1.
[*]The focus assist mode 2 blows away the NEX 7.
I would upgrade for things like a larger sensor, more resolution, better high ISO, better DR, and/or slightly better resolution, but not for FD, PK or M42. I wouldn't buy a mount in these formats, at all. If they could improve the mount itself, they could use a short register mount to be more universal and use an M-adapter to mount M lenses. However, the NEX-7 that I'm borrowing has a very sloppy adapter, whereas the GXR-M is rock solid.
Right now I have only bought 2 of the many adapters already available for the GXR, an EF adapter so I can shoot tilt-shift and an MD adapter so I can use some of my fast and long MD lenses. The Pen F lenses work great, even if I just hold them on with my hand, so I'll probably buy a Pen F adapter, too.
Collection: GR1 GR1S GR1V(date) GR10 GR21 R1 R1S R1S(gold) R1E R10 RX60 GRD I-IV GRD Ltd GX100 GX200 GXR A12-M G4-Wide 500ME