I use my MF backs on an Alpa or an Artec. I use an S2 like an SLR. At the moment I have an as new D3 sitting in its box with a bunch of equally boring Nikon lenses in their boxes. Happy to have the hassle of a tech camera to make tech camera shots.
@3k for a new body that provides the utility of this new generation camera is not a big deal in the scheme of things- maybe less than half the cost of one S2 lens so I might cough up for one.
People that use MF backs tend to understand what 35mm cameras are good for and what MF backs are good for.
The idea of one camera to do all things - exists only in the mind of people who dont really do much shooting as far as variety goes.
One thing that has become apparent over the years is that it is very easy to collect stuff - especially new fangled gee wizz stuff from 35mm land - these days pretty much any camera one purchases is very capable of making nice snaps. If you want something a bit better than a nice happy snap - well you need to put up with the hassle of MF etc.
one aside- if anyone thinks that a 35 megapixels on a 35mm sensor is going to be an easy camera to handhold and get decent results- you may be disappointed.