I still refuse to believe this is all the characters. No Birdo, no Bowser Jr., no Diddy Kong (or Dixie or Cranky). But now I'm starting to think they'll be DLC, like in Mario Golf: World Tour. Say for $5.99 you can get a cup of four retro courses, some new kart parts, and Diddy Kong (and maybe actual arenas for battle mode?), or $19.99 to buy all four packs at once plus unlock Emerald Luigi, who is immune to Blue Shells but can't use any items himself.
That would kinda suck since they did explicitly confirm in the ND that it's $60. Mario Golf is only $30 (in America. In Europe, it's still full price for a 3DS game, which is noticeably more than USD$40 already), so getting the game with the season pass gets you a pretty huge number of holes for only $5 more than a regular 3DS game (if you're American), even if those extra holes are just the courses from Mario Golf 64 with new scenery.