I think this overplayed "dark version of character" trope would have spread too far in the Mario series and I'm glad Nintendo kept it in check, whether that was their actual reason for it or not.
Mario having an evil version of himself was a matter of course. He's basically a superstar both out and in his fictional universe, so he'd obviously end up attracting vain imitators (and what we got was executed superbly).
Waluigi was created more out of a gameplay necessity, but I can tolerate the concept. Though, he would have been more interesting if Nintendo went through with his designer's original vision, that is to make him this sharp-toothed, cruel, unrepentant, atrocious monster and professional son of a gun who lives to do bad stuff like how Wario lives for money.
Carrying their torch further with Walpeach would've been unwarranted, nevermind that her design needed some work to become proof of concept imo. Interesting piece of history, though, but not every single character in Miyamoto's holy garden needs a bizarro counterpart.