If such camera appears it won't be probably made by Leica in Solms/Wetzlar, but outsourced somewhere, as it's surely the case of the X1. Even this way, I'm afraid it will be rather expensive -on line with Leica's pricing.
Anyway, with a M mount, you have access to almost any 24x36 SLR lens ever made. There are adapters for M to R of course, but also for other SLR mounts and companies like Novoflex and Kipon are willing to produce adapter rings of any kind, provided there's a fair market for them.
See what is happening with the Micro 4/3 format, you can buy adapters even for lens mounts so long discontinued as the Swiss Alpa.