This. There was a lot of creativity and originality in Mania, but it was kind of overpowered by all the nostalgia it had going for it. Which is fine, since we haven't had a good 2D game since the Rush series concluded (and even then, that series wasn't traditional 2D at all, you have to go back to the Advance trilogy for that), but I don't think you can effectively milk that for more than one game without it feeling cheap.
Give the Mania team full creative liberty to do what they want. HD visuals, all new stages, all new ideas. Mania is one of the best games of 2017, I have no doubt they'd knock another game out of the park with the same foundation.