Canon Japan has just filed a new patent about Canon mount, this mount is neither EF or EF-M mount. According to previous rumors, this could be the new mount for Canon Full Frame Mirrorless cameras.
From Japan Patent Application 2018-084713:
Conventionally, the serial communication (synchronous serial communication) of a clock synchronization system has been adopted as a communication method of a camera and an interchangeable lens. The following technical contents are disclosed in the Patent document 1. First, synchronous serial communication is performed with the first communication speed with which an interchangeable lens old type can also communicate. When the interchangeable lens with which it is equipped is distinguished from a new lens by the communication content, it changes to the synchronous serial communication in a more nearly high-speed second communication speed.