A Canon patent spotted by Canon News at the Japan Patent Office, suggests that Canon is looking to downsize their in-body image stabilisation system to make it smaller. While IBIS has obvious benefits, the drawback is that it takes up a lot more space inside a camera than simply housing a static sensor.
This might be why Canon hadn’t implemented IBIS into any of their mirrorless cameras before the launch of the EOS R5 and EOS R6. It simply made them too big. This patent might be for upcoming EOS M system cameras or simply to make future full-frame EOS R cameras a little smaller and lighter while still retaining the IBIS functionality.