Interesting thread.

I hadn't thought of it in the past, but I also think the Bronica S series would be good. It can accept a wide variety of lenses. One could easily have a "lens-board" made that would screw into threads purposely made available for this purpose where lenses connect to the camera's bayonet mount system. It has the focal plane shutter, but one could then also use a lens with a between the lens shutter. As someone else pointed out, the Type II bellows has some movements.

A potential problem is the "violence" with which the shutter on these cameras exposes the film when using lenses without shutters. There's no mirror lockup with this camera. But, I would think this could be mitigated by strong support and by the fact that macro requires long exposures. The time period during which the shutter opens is very small, when compared to the overall exposure. Plus, I've used an S2a for years, and I get very sharp photos. This would not be an issue when using between the lens shutters.

By the way, what's the advantage of the focal plane shutter, other than this would make it possible to use a wider variety of lenses?