Bowser Castle - Mario Kart series
Way long overdue.
The Stage - Paper Mario: The Thousand-Year Door
Eldin Bridge's shape with hazard extravaganza.
Any new area from DKC2 or Tropical Freeze
Really, any location that isn't a jungle would be welcome, especially if it comes from those games.
SkyTown - Metroid Prime 3
With how unfairly omitted Metroid Prime 3's representation was in Smash 4, this stage would be a great way to recover this fault, not to mention Steamlord hazard and stuff.
Sector 6 (NOC) - Metroid Fusion
This would be the new "Temple" of Smash, as to know an unexpected stage from a less relevant but cult game.
Not to mention both the look and hazard potential (like destructible elements and X viruses) would constitute a great breath of fresh air for a series which mostly consisted of lava-themed places stage-wise.
Aurum Islands - Kid Icarus: Uprising
I know it would be the
third time Uprising would be repped stage-wise, but I don't really care, this location has lots of potential to be a cool stage.
Sylvalum - Xenoblade Chronicles X
Rather than "lol all Mira Delfino-style", I would just want this place from Xeno X, as it easily has one of the most unique aesthetics in gaming.
It would be also interesting to see a certain gigantic boss from the original game, which appeared there, appearing as an hazard as well.
Excitebike Arena - Excitebike
After Wrecking Crew, Pilotwings and such, it's time for another classic retro title which can hardly have playable representation to shine.