That's what a Canon patent application seems to suggest, a 300mm f/2.3 mirror lens. Read…
Yet Another Canon Patent For IBIS (In Body Image Stabilisation)
This morning we posted a Canon patent application discussing a triple image stabilisation design, and here is another patent application discussing IBIS (In Body Image Stabilisation).
Canon patent application 2019-0191089 discusses an IBIS unit which could well find its way into a future Canon EOS R model.