I kind of think that would be weird because adventure time is just one of those shows that has it's own world and backstory and it would be strange if regular show would suddenly pop up into it, i think SU and UG did it because they are kind of just random shows with just no meaning so it didn't really effect it's story line at all, not that i am saying that they are bad shows or anything.

I feel like that regular show is another dimension since they have anthropomorphic animals which could have been from the great mushroom war

That is a good point that would be cool, but then that would mean that regular show is just another side to adventure time, but the shows do have similarities to it, and what your saying could be possible

Unfortunately, Pen Ward does not want a crossover with another show.