I think you could yes. In the modern series anything goes. And that's one of the major problems with it for me. But yes, you could say that there is an alternate earth where superheroes exist - we saw in David Tennant's era there are alternate earths with very different histories, so that is one possibility for doing another such superhero story.
It's possible that the Whoniverse, the MCU, DCU, Star Trek, Star Wars, and just about any other book/film/franchise you could mention all exist within the same infinite multiverse.
yes, inside the Omniverse!