Waluigi needs a role in a real Mario or Wario series game before he can be playable in SSB. A role for him outside Mario spin-offs is long overdue, he could easily be a playable character in a New Super Mario Bros. or Super Mario 3D game, or a villain in a Luigi's Mansion game, or a partner in crime in a Wario game etc. Even a minor role in an RPG or other main series game would be fantastic. Waluigi is a character with a lot of untapped potential, he's one of the most unique characters in the series and absolutely oozes personality. Why Nintendo have shackled him to the spin-offs all these years, refusing to let him anywhere near anything else is pretty bizarre in my opinion, even Toadette, an extremely generic character (just a female Toad) who was only made for the sake of Toad having a partner in Double Dash (yes I know the reasons for Waluigi's creation were similar) got a role in an RPG game and a cameo in Galaxy. C'mon, do something with Waluigi, Nintendo.