Keith,
Yes, M bodies always have been mirrorless, Visoflex not included, which is why nobody thinks of them as such, but simply as digital rangefinder cameras. So they represent nothing new in the sense that "mirrorless" will represent for other manufacturers such as Nikon. Nikon did make rangefinder cameras too, eons ago, and I believe they even went the Leica route and made a celebratory run of one of the S bodies, complete with lens. Nevertheless, to all practical extents and purposes, Nikon history as remembered and perceived today, begins with the F slr, the opposite to Leica heritage.
I have seen through either a Fuji to Sony with evf - can't remember which brand - and it was "similar" to a normal dslr system but in a rangefinder-styled body. But no way did it feel the same. I think the viewed image felt even smaller than my digi Nikon D200 and obviously not as good as the ff D700. And peeping into an eyepiece way off the lens centre line didn't help much - also something I find horrid with the cellphone.
Okay, there is live view, but that also exists on dslr bodies, and not something I have used other than once when I photographed my apartment. If one's work demands much of that, then maybe 135 format bodies are far from your best buy.
I suppose nobody, not even Leica, knows what to do for the best. As a company, it has been rescued and refinanced time after time; that doesn't indicate anyone new had a better idea than the one before, just that the magic in the name makes belief in a better "tomorrow" possible. Taking that into consideration, along with the febrile fan base, I don't think that something like an improved R6 would do them any harm. As an object of desire, the later bodies resembled nothing as much as they did my two ugly old Exaktas, not exactly the most chick of shapes! And yeah, you apart, I think the perceived glamour is what draws the majority of buyers to dig deeply.
Actually, if you are going to have a rangefinder body and like digital more than film, there is not a lot to dislike about Leica! I have often wondered why Nikon and Zeiss didn't go there too, though having flogged off the Contax brand, it might be difficult or Zeiss. They did make a very good rangefinder at the end of their film camera days; some thought it superior to the M6 or whatever was current at the time.
Rob