Personally I think it'd be pretty cool if Pizza Tower or Anton Blast got crossovers with Wario Land, given how heavily inspired by the latter they are.
Yes, put Wario in everything. He already crossovered with Starfy and Bomberman. Nintendo let Zelda crossover with Cadence of Hyrule, they should let Wario crossover with the Wario-like platformers.
Wario in indie games would be great, even if they are set apart by their differences. Having him playable and doing his regular platforming and sidescrolling shenanigans and maybe some new moves or transformations would be the easiest and simplest way to make Wario fans happy without a new game.