Actually, someone mentioned "Sinar M" in another thread in another context, which actually comes pretty close to my speculation as a rough sketch:
Sinar
Note top of page "A Jenoptik Company" - and who just completed a digital imaging cooperation agreement with Jenoptik in June? - our buddies in Solms!
http://www.jenoptik.com/cps/rde/xchg.../5705_6277.htm
If the Leica S2 turns out to be a rebadged Sinar M straight up , M lenses might be tricky - but the modularity likely means it would be possible with a Leica-only module for the short backfocus.
I'm suddenly getting a really warm fuzzy feeling here....
http://www.sinarcameras.com/file_upl...system2005.jpg
Note that the Sinar M currently takes Nikon-mount lenses - a little screwdriver engineering could make that an R mount....or, without the extra thickness of the reflex module, an M mount...
Oh, and Overgaard...yes the Red/Scarlet system occured to me also as an example.
I just LOVE system cameras. Even when I used nothing but a plain prism I LOVED the interchangeability of the Nikon F and Canon F-1 systems - something Leica SL/R always lacked: backs, prisms, screens, motors, waist-level viewing - build the exact camera YOU want - or field strip it just for the heck of it.
Now - if only the Sinar focusing screen is up to Doug Herr standards.....I imagine he can lean on Leica to make their own if not.