Very true. It's possible.
Though in the end, the actual problem is how much licensing to do. Sakurai was clear that it was very difficult to get this many 3rd parties together, and doing so again wouldn't be easy. A port alone is probably not likely due to that factor. Now, a port with all the Nintendo characters, all the Pokemon(technically speaking they're 3rd party, but nobody counts 'em that way. Being partially owned by Nintendo is important, after all~), and some easier to get 3rd parties(Sega, Capcom, Microsoft, at the very least, and Bandai-Namco I'm not sure would be beyond Pac-Man. Kazuya is probably safe?), along with tons of new Nintendo characters(like, you know, Dixie?) sounds good.
If this is a thing, it could be under a new Director. That means anything could change. Odd alt costumes(clones and echoes being reduced to this position), any old guidelines Sakurai follows being changed up, etc. For instance, Sakurai surely has some moveset ideas for characters not used yet. Or at least we have a confirmation it was a concept that was wanted in Dixie's case. Whether he actually cares about the whole tag team gameplay or not would mean little with another director. Maybe he does, maybe he doesn't. But let's say he does for this hypothetical(no, I am not saying for sure he does, obviously). Now, we have a new director. They aren't going to have the same visions. These types of things are very different from other guidelines. Not changing movesets too much cause they alienate players? This'll probably stay on the other hand. Stuff like Echoes having rules about how they work(same bodyshape overall, with at most a pixel difference, same weight, same attributes) could change. They could re-label numbers and call any kind of Model Swap Fighter an Echo. It's silly, but that's how much could change very easily.
This is probably why people seem to be more interested in keeping the same director. Throwing out the normal stuff through the window can make things awkward. Of course, there's fans who want these changes and that's fine too.