Leica M distance, flange to sensor: 20mm. Nikon Z distance, flange to senor: 16mm.
My guess is that most want infinity focus on adapted lenses and unless there's an optical adapter to allow this, a market, etc., it may not happen. But that's just speculation on my part! ;-)
From what I've read by users, the lens selection from Panasonic, Leica and Sigma are comparable to the selection from Nikon in IQ and you won't need to putz around in file processing since part of the Z system lenses have software image correction enhancing some of the lenses as to physical limitations and issues such as distortion, CA, vignetting. From what I understand, it's a synergy of balance between optical perfection/size/cost vs. easy software tweaks of the image, the best of optics and electronics.
