That Canon’s next R model will be a High Megapixel camera is 100% certain. Latest unconfirmed rumor is that this camera will be announce in late 2019 and feature a new 70+ megapixel sensor and IBIS.
I am pretty sure both Nikon and Sony will have such a model release too. We are getting slowly closer to the 100 megapixel barrier. Get ready to buy a ton of external hard drives :)