Canon is showing off a teleconverter that can switch between 1.4x and 2.0x, which would be a great way to increase the usability, flexibility and efficiency of using teleconverters.
If you’re on location with both Canon teleconverters, it adds to the risk of dust getting inside the camera body. If you’re switching between 1.4x and 2.0x teleconverters, you may also miss the shot.
Adding teleconverters to big lenses increases the size, weight and bulk of lenses as well, so simply putting built-in teleconverters into every super telephoto lens probably isn’t the answer either. Canon has been working very hard to reduce the size and weight of their big white lenses.
I couldn’t figure out in this patent if you could also switch to 1.0x, so you could, in theory, leave the teleconverter attached to your favourite lens if you so desired.