RTD need to bring back Gallifrey(again) somehow so we can get hopping between reality’s like described in age of steel/rise of the cybermen. The multiverse has so much potential. Yes the multiverse is “the thing” right now but doctor who has the ability to do it best. With multiverse travel we could have so many episodes with catastrophic world ending conveniences but the doctor couldn’t do anything about it. I mean look at season 7s inferno.(spoilers) The 3rd doctor accidentally travels to a parallel detention where the earth gets destroyed giving him the knowledge on how to stop the world being destroyed in the main timeline. There are so many possiblitys with the combination of time travel, space travel, and the multiverse

Edit: we’ve already seen this work outside of the Cybermen episodes. Turn left explored an alternate timeline where Donna never met the doctor. Now imagine other stories like that following what happened if key events in history were changed. Like if Archduke Franz Ferdinand was never assassinated. Small incident large effect.