Woe: Pokemon Stadium 2 is my definite. A lot of the stages I think will get new versions that better fit the new games (such as Luigi’s Mansion, Mario Circuit, Smashville, Kid Icarus stages, etc). However, a lot of the Brawl ones will probably return though, including Smashville, possibly WarioWare, etc. Maybe 75m and Mario Bros too as special stages.
Volcanic: I agree about Pokemon Stadium 2, and that most stages will get new variations with franchise updates (like new Smashville, new KI, etc.). If we have to go with 10 stages from Brawl returning, then I can see Delfino Plaza, Pirate Ship, Battleship Halberd, Lylat Cruise, WarioWare, Norfair/Frigate Orpheon, Castle Siege, New Pork City and Yoshi's Island returning, but the only stages I would DEFINITELY rule out are the Spear Pillar, Distant Planet, Flat Zone 2, Hanebow and the third party stages...