I've been giving this idea of taking both mounts in the same camera some serious thought and I've come up with the answer. Put the RF mount directly in front of the sensor in the normal way. Then.... put the EF mount off to the right with a series of mirrors going over to the sensor!! If an EF lens is detected, the final mirror swings in front of the sensor, routing incoming light from that mount. This avoids all that troublesome problems with the moving sensor that others have speculated about. Genius!