Myself, I have both an R and an L. Maybe it's just me, but most of the time I only go out with one body or only carry one. If I'm in such a rush to change lenses out quickly, I take my SLR. It's bayonette mount and I have more glass for it anyway. Perhaps an R2 with a few LTM to M-mount adapters would be more what you're looking for. It would be the most complicated, though and probably cost the most. Sell the R, skip the 90, save all the money, and buy an R2.
My $0.02