Canon patents a mount replacement camera system, which is likely related to the soon-to-be-released Cinema EOS C700 and an already available service for the Cinema EOS C300 Mark II. I'm not sure if there's any reason for this on a DSLR.
Patent Publication No. 2016-192701 (Google Translated)
- Published 2016.11.10
- Filing date 2015.3.31
- Mount exchange possible
- Change the menu content depending on the mount
You can read about changing mounts for the Canon EOS C300 Mark II at CPN.