The Smash series has at least 50 unique stages – It’d be nice to see all of them return over time. Seeing that Splatoon 2 has brought back more than half of the stages from Splatoon already and how Nintendo has been embracing downloadable content, it would at least be nice to see all stages return over time.
Bar time constraints, there isn't really much of a reason not to. In theory, at least, it's easier to bring back stages than to create new stages. Most stages, no matter how weird or simple, are someone's favorite. This does come with one problem, though: leaving people overwhelmed with the amount of stages.
With the possibility of downloadable updates, it's very possible to see stages not only fix that but keep the game's lifespan going for longer while still feeling fresh
Author's Note: What stages do you want back? Let us know in the comments below!