The only way they can keep the format the same and within an hour, with breaks, is to cut all the history stuff, all the bits of contestants talking to camera about how they're feeling, all the deliberation bits between judges in order to make time for 3 bakes a week.
Which wouldn't be keeping it the same at all. Paul Hollywood has already confrmed he'll be hosting a car/travel show for BBC2, and Mel, Sue and Mary aren't automatically part of the package either. Mel and Sue are a good fit for Channel 4, not sure about Mary. Bake Off without Mary and Paul isn't Bake Off though.