I'm not usually the cynical type, but if Nintendo hasn't introduced him in the latest games, then i'm not feeling very hopeful for a appearance at the current moment.
Wario Land & Warioware for all intents and purposes have always been seperated from the Mario games in every way possible. and despite what Super Smash Bros. or Sakurai says,
Waluigi has always been a Mario character first and foremost rather then a Wario character. he debuted in a Mario game and even to this day he only appears in Mario titles despite Nintendo having many oppertunites to have him in the Wario games,
Like why wasn't he playable in Smooth Moves or in any of the recent Warioware titles? they have had so many chances and oppertunites to do so, but they never have once took them. will he appear someday? maybe, i've definitely been surprised before, but his chances of appearing in anything outside of Mario Party, Super Smash Bros, Mario Kart & the all the Sports spin-0ffs is pretty much non existent at this point. Hell even MK7 didn't have him, and that's a fucking Mario Kart game where he has always been a mainstay in. sure he comes back in MK8, but the fact that Metal Mario and Queen Honey Bee were given higher priority over him alone shows how relatively unimportant Waluigi is to Nintendo as a whole. and that really sucks, because i want to see him get more love not just in the Wario titles, but in general. he's a fun and wacky character who has a lot of potential to be just as interesting as Wario. (Look at Brawl in the family for an example of what i'm talking about.) but it seems that currently outside of the above mentioned titles, Nintendo basically pretends that he doesn't exist and that is just sad. maybe someday, Nintendo will give him the love that he so properly deserves, but right now, i'm not too hopeful at the current moment.