I think some WarioWare character could fit in a Wario Land game as side characters. Like for example having Mona giving Wario tips since it's said she goes on treasure hunt with him.
I believe they can easily share more elements with each other at least.
Like a WL game that contains microgames inbetween worlds as interludes. We'd have a mini WarioWare within the game and typical modes you'd expect in the postgame. But...
Found on the Super Smash Bros Ultimate subreddit. with a mix of Wario Land and WarioWare moves, a Wario Land stage, a mix of songs from both series and more characters from each:
I'd personally be okay with it.