In fairness to Leica, I don't think this system is aimed at amateurs, so they can be forgiven for not making used lenses available for it. It is being designed from the ground up.
As for Rollei, I guess I am a bit more picky. Most of the lenses are very very good, but I am not extremely happy with the 40mm -- there is a lot of distortion (to my eyes), and it is not very sharp at f/3.5, f/4 or f/4.5. The corners don't get very sharp until f/11 I would say. I do like the size and ergonomics though. As for the other lenses, the 80mm is faultless. The 150 Tele-Xenar is excellent, though focuses only to 1.4m. It is better than the 150mm Zeiss, which is still good, but not as sharp, particularly at f/4. The 110/2 is superb, but of course it is not beyond reproach wide open (its look is, but objectively it is not great other than in the center when used wide open). The 180/2.8 is very good from f/4, though it is a monstrous lens (same with the 110/2). I have not used the others. None of these lenses are as technically spectacular as, for example, the APO Leica lenses, or the ASPH wide angles....the R system too, so not just the M lenses. For this reason, and the fact that they will not have to use as large an image circle, I suspect that the Leica lenses will be significantly better.