The Waluigi roleplaying aside, my unpopular opinion is there aren't enough Mario characters as a whole.
Yeah, we got a whole bunch of them but very few series have such a huge cast of beloved and colourful characters that are instantly recognisable to millions and millions of people.
Put Waluigi in. Put Captain Toad in. Put Toadette in. Put Paper Mario in. Heck; put Pauline, Nabbit, E.Gadd, King Boo, Fawful and yeah, Geno and Mallow in. Heck, I wouldn't be sad if we got a few more iconic minions in such as Koopa Troopa, Boo or Goomba...although preferably after the likes of Toad and Waluigi at the very least make it, thank you.
No Baby or metal versions though. That's a step too far Nintendo. I'm watching you with your Dr. inclusions too...