Tim,
I'm currently using the new
Arca M Line 2, which is a great camera and will be my work horse for studio shooting and long lens shots. I borrowed the Rm3d from Arca for about a week and I can see advantages for using it when trying to work a little quicker (say on exteriors) or when I want to be un-tethered. I have rented the Cambo RS on numerous occasions and think it's a fine camera, well made, compact and easy to use. Still, I prefer the Rm3d with it's built in tilt, higher resolution focus mechanism and sliding back capability. Plus I can swap the lenses back and forth with my view camera.
Jonathan,
That's a good question that I expect to discover the answer to soon. I'll do a full review on the R at my blog and will assuredly discuss the modularity between the systems.
Cheers,
CB