I think the key word here is "professional". Professionals who use the digital Ms exist, but they are maybe not that many. From a professional you get opinions such as Roger's, which, as I understood it, basically seems to be "as long as I still get the compact reliable rangefinder I use for my work, it's fine whatever they put in there".
However, from the non-professionals you get opinions such as "Image stabilization? I might just as well buy an SLR". Here you find people who buy a Leica not for what it gives them, but for what it isn't. For those people, digital developments pretty much end with the M9. What can Leica do for the M10 that competes with tomorrow's cameras, so as not to spoil it for this segment of their target demographic? Put another different sensor in it and that's it. Of course, innovation and engineering end here, but then again, for people averse to progress this means heaven.
If that works as a business model, by all means go ahead, but we have examples of camera companies where it didn't.
I think Leica is seeing the world pretty much as you describe it, or else they wouldn't have developed the S line. That is mainly geared towards professionals who see the logic, while not "different" and 1950's-style lacquered-brass-authentic enough to be interesting for "advanced amateurs" (or, to put it polemically, bobos and affluent pentagenarians+). I think it's a good idea for Leica to have a second leg to stand on camera-wise. Some engineering and development has to go on, otherwise it's just stagnation. And then you end up like Rollei, with a name slapped on dime-a-dozen Chinese compact cameras, ballpoint pens and lighters, and an assembly hall somewhere where people put together 1950s-style TLRs from leftover spare parts to sell under a different name.