Ebay seller sigmacumlaude is offering mount replacement kits (Leica R, Nikon F and Olympus OM mounts) for the SD1/SD1M.
Although the viewfinder is not the best for manual focusing, and the screen is of no help whatsoever (no live view), there used to be a community of Foveon fans who were inclined to shoot Leica R lenses on the older SD bodies, so much that the replacement mount specialist Leitax took the plunge and issued a dedicated bayonet.
However, Leitax does not offer any adapter for the SD1. Sigmacumlaude’s solution seems to be the only way to mount non-SA lenses on Sigma’s latest DSLR.
Probably well worth a try is the Nikon F-mount adapter with Zeiss ZF2 lenses. Similarly to the sweet Leica R lenses, they are ideally crafted for manual focus, and some of them have no “equivalent” in Sigma’s lens lineup. In particular, I’m intrigued by what a 100mm f/2 Makro-Planar or a 135mm f/2 APO-Sonnar can do combined with the sensor of the SD1.
If you have tried or plan to try this mount replacement kit, a feedback would be greatly appreciated.