Sonic Movie 1: establishes how this world is different from the games
Sonic Movie 2: more references and moves towards the games canon more
Sonic Movie 3: about an iconic, fan favourite rival to Sonic
Mario Movie 1: establishes how this world is different from the games
Mario Movie 2: more references and moves towards the games canon more
Mario Movie 3: cautious optimism
Well that and Wario seems like an obvious choice for the third movie. There's never just one or two unexpected characters per film, and with Daisy as one of the newcomers, logically Wario could be another one.
Honestly the only thing that'd make me feel pessimistic would be if the post credits scene was Mario getting a letter as a Smash teaser or something, but luckily that didn't happen. I'm not against the idea, but I just think it'd suck if it was no longer about the Mario series before Wario even gets a chance to shine
Daisy, Wario, and Waluigi all follow a rival theme to Peach, Mario, and Luigi. Daisy also doesn't really have a lot of backstory outside of Sarasaland and instead leans heavily on personality just like Waluigi. And with Wario being less relevant and primarily being Warioware nowadays, I feel like Waluigi is starting to get slightly closer to having the same level of popularity and recognizability as Wario.
So with that in mind, and the fact that Wario and Waluigi thrive as a duo, I feel like between the 3 of them, they'd all have the same level of popularity, priority, impact on the story, etc. so I can totally see Wario and Waluigi making it in. And also because there's not a lot of other candidates for the main cast that are well known by the general public
