This is the big question: where's the market? There's a very small market segment that doesn't want/like modern 'conveniences' (auto exposure, autofocus), but which either can't afford an M-series or prefers to save money by buying a camera they don't really want (typically a DSLR).
This tiny market segment is sandwiched between the huge majority who want idiot-proof auto-everything (some of whom even want to ruin Leica Ms by adding autofocus) and a small minority who buy Leicas because they really like cameras without unnecessary bells and whistles. Ronald M sums it up very clearly.
Also, where were these 'reasonably priced' interchangeable-lens rangefinders? Especially after the mid-1960s? There were increasingly outdated and increasingly agricultural FSU designs, but basically, the 70s, 80s and most of the 90s were pretty much a dry spell for decent RFs until the Voigtländer name was reintroduced, followed by ZI -- and it's a LOT cheaper to develop a film RF on an existing chassis than to develop a digital RF from scratch. The few other reasonably high-end film RFs that showed up in the 70s, 80s and 90s were failures (or their manufacturers would have kept them in production longer). Where's the incentive to bring out a new digi RF that could at best compete in price with second-hand M8s?
Cheap fixed-lens RFs were popular because they were the cheapest way to get your pics in focus, reasonably reliably. Autofocus is now the cheapest way to do it. The moms and pops ain't gonna go back to fixed-lens RFs; there are several modern autofocus equivalents; and you can't even get (new) leaf shutters cheaply and easily any more. And yet, the fantasy keeps surfacing.
Cheers,
R.