This would be, I think, the primary conundrum that faces Leica, whose products have been sold on the basis of their extended durability. A digital, because the life of the technology is significantly shorter than the lifetime of the mechanical aspects, doesn't necessarily need to be as durable as an M2. It may need to be durable enough to withstand the demands of professional use, if it is indeed a professional tool, but it doesn't need to last 40 or 50 years because the technology inside will only last 5 at most. But durability is one of the keystones of Leica sales, so creating a camera that would allow them to offer timely upgrades in keeping with changes in technology ala Nikon & Canon would inevitably affect that keystone and thus the company philosophy.
In other words, put a Leica M mount on Panasonic G1 technology stuffed into a rectangular body & you'd sell a stack of them. Plus you could upgrade to better faster more beautiful technology every 2 - 3 years with a G2, G3, G4... without your customer base having to swallow a $4, 5, 6, 10,000 price tag.
But you wouldn't necessarily be the same company either.
I'm glad I am not trying to run that company.