Neither the Sony A7 nor its A7R sibling are particularly friendly to rangefinder lenses; it’s the ray angle at issue and it causes all sorts of image quality losses, from color shifts to sharpness to white balance.
Moreover, DSLRs have too great a backfocal distance to be useable at all with rangefinder lenses, so mirrorless is the only hope for a wide range of some very fine lenses, Leica M Typ 240 aside, with its out of reach price for most photographers.
Suppose the landscape were to change, e.g., what if sensor technology were to evolve such that a 36 or 50 or 60 megapixel mirrorless camera were to appear with a sensor that by design is far more friendly to ray angle, perhaps even made usable for the worst case lens, the Zeiss ZM 21mm f/4.5 C-Biogon with its demanding 44° chief ray angle?
After all, the Leica M9 and Leica M Typ 240 already do have sensors that are relatively friendly to rangefinder lenses. That further improvements might be in the pipeline is well worth pondering for anyone with a stable of Leica M or Zeiss ZM lenses, e.g., some patience might be worthwhile.