I am not the OP but tested a few of my Leica M-mount lenses on an X1D.
First, a special case is the AstrHori 40mm 5,6 which has an M-mount but is designed for 44x33 coverage. It does indeed cover the whole sensor with moderate vignetting and is quite sharp corner to corner.
From my more traditional lenses, the only one which gave decent coverage without hard mechanical vignetting when stopped down was my Summulix 50 1,4 ASPH. Still, corners were quite weak.
All my other M lenses (18mm Super Elmar, 28mm Summicron, 50 2.5 Color Skopar, 75mm Summicron, 90 Elmarit) showed a clear lack of coverage with very dark or even black corners, the 75mm being the most usable from the bunch, with stronger vignetting but sharper corners than the 50 Summilux.
Now, most (apart from the Super Elmar) could probably be used with a 1:1 or 24:65 crop and stopped down a bit, but shooting adapted lenses in ES mode is a bit of a pain as illustrated in this thread. You have to keep the camera perfectly steady after the EVF blacks out. I did not find the experience pleasant or even natural. But for still shots on a tripod, it is certainly an option.