I'm kind of against Waluigi showing up in either Land or (more likely)Ware. He just feels too much like a Mario character to me and it would feel like inserting more Mario stuff into DKC than there already is.
That being said, I would be open to seeing Waluigi with Wario in a new original game of some kind.
If Waluigi ever got in Warioware, I would assume his microgames would be about causing "evil" schemes. Like how Wario's is mostly about treasure hunting and eating food, Waluigi's will be like...tripping over an old lady?