There have been a couple of Canon patents for TC solutions recently, one quite recent where some elements rotate and slide out of the way in different locations that looks like a two-option solution (e.g. 1.4x + 2x switchable, or perhaps 1x=bypass + 1.4x or 2x). There was another from a couple of years ago with what looks like 1x+1.4x+2x (or a TC zoom) with the ability to also add drop-in filters and maybe a kitchen sink, but that one does not look like something that would be made into a product (in theory it could, because of course 'reduction to practice' is needed for a patent, it just seems rather impractical).