I do not have, and have never used, either a Monochrom or a GXR with M module (nor any other module). Nonetheless, my vote is for the M type 240 because that's what I did. While in theory I loved (and love) the concept of the Monochrom I also shoot in colour and so could not and cannot spend that much money on a mono-only body, especially when all reports (and subsequent experience) show that B&W conversions from the M240 are pretty good (if not, quite, up to the standards of the native B&W from the Monochrom). Give me the dollars, and I'll have a Monochrom side-by-side with my M240. But given the only way and reason I could afford the M240 was by a bequest from a favourite uncle, that just isn't going to happen.
I won't touch the GXR-M simply because I'm an optical finder bigot. Sue me, but I just can't get along with any kind of EVF, at all, ever (or, at least, so far). It's not that I reject the concept, it's just that I can't personally get along with them. I would have loved, for example, to get along with the Fujifilm XT-1. Many told me I would, and told me that this time the EVF was so good that even a bigot like me would love it. I didn't. Not even close.
I did buy an EVF for my M240 (the Olympus-branded one; I'm not paying Leica prices if I don't have to). Not because I've used it (aside from testing it when it arrived from the wilds of eBay) but defensively, to make sure I might still have one long after they might be superseded (which something already obsolete on introduction might well end up being). Aside from that one test, I have a "Thumbs Up" permanently mounted on my camera (precluding the EVF) and that's unlikely to change. The OP may be "..betting on lots of people getting a Leica M and mainly using it with the EVF.." but that sure isn't me, and never will be. I would never ever have paid so godd*mn money for a digital Leica if it weren't for the optical VF/RF. That, to me, is the only reason for it's existence and the only reason I bought one and will keep it 'till it dies or I do.
...Mike