Here's a strange patent application from Canon, an optical viewfinder adaptor for a mirrorless camera.
Canon News breaks down Japan Patent Application 2018-005126:
This adapter would provide the half mirror assembly that would split the optical path between the image sensor and the viewfinder, and allow for simutaneous use of the image sensor and that of the optical viewfinder.
The image sensor would be responsible for AF for one embodiment, the other embodiment has a seperate phase detect AF sensor.
There is a large group of photographers that just don't like EVF's and may never like EVF's, so this could be a solution for them.
Me personally? It wasn't until the Leica Q that I got over my hate of EVFs.