@Koopaul- Review of your choices
1- I agree about Waluigi's lack of role, but he shouldn't really be first on the list. There are better characters to put here.
2- Daisy is same with Daisy? What the heck does that mean? I'll assume you mean same with Waluigi, which I COMPLETELY DISAGREE WITH. Daisy, unlike Waluigi, has a set role in the Mario universe. In fact, I wouldn't mind if she made less appearances.
3- I agree that she should get into the action more, but I think it should be a PM-type deal - that she infiltrates Bowser's Castle from the inside. I just don't see her running and jumping alongside Mario in a main-series game, unless it's Subcon-related.
4- ABSOLUTELY NOT. Yoshi is already one of the biggest characters in the whole series. He does not need more screen time, especially if he already has a series of his own. With Peach, it's different, because she's almost never playable. But, come on, Yoshi? He would be 11th on my list, tops.
5- COMPLETELY AGREE. Tatanga was a great villain that could be better utilized than he is now.
6- I would love to see them outside their respective series, but I don't think it would really work if they left the RPGs altogether. I could see a PM character in a M&L game, or vice versa, but not in another type of genre. But I could be wrong on this one.
7- See #5, and replace "Tatanga" with "Wart".
8- See #4, and replace "Yoshi" with "DK". However, I'm a little more lenient on this one. He could use more screen time, just not in the Mario series.
9- Bowser has a set role in the Mario universe. That is being a villain. I could see a Despicable Me-like game, where you play as Bowser trying to kill Mario, but he should by no means turn into a major hero.
10- Agree somewhat. Birdo is underutilized, but I still wouldn't make him/her a major character.
I also noticed that you neglected to include Toad or Toadette on your list, two of the most underutilized characters ever devised. Toadette would even probably be first if I made a list like this.
Which I might.