Digital photography is still at its infancy stage, and it will be interesting to see how it progresses over the next decade, let alone beyond that. Still, affordable digital systems, and I'll arbitrarily define that as up to US$3,000 (which is beyond my personal budget), are limited to DSLRs and compacts. It is questionable if certain systems, including the medium format Holga, the TLR, or large format, will ever make the digital conversion.
For the vast majority of photographers who only shoot digital, the loss of these systems as an option is likely inconsequential. However, I look forward to trying most of these cameras, as they each add a different approach to the photographic process, which to me is as important as 'getting the shot.' I can point an SLR at a stranger on the street, but it's a bit easier to do with a rangefinder. I would assume that using a square format 6X6 medium format would pose its own set of unique compositional considerations, and no, cropping precious resolution from a digital shot would not be the same.
To be sure, I'll be looking to see how digital quality advances, but a digital rangefinder that produces black & whites with the depth and resolution of its film counterpart and for, say, under US$1,200; probably not for some time.