Would casuals really care about those characters though?
I'm not sure they would. For actual fans, yes, they're must haves, but for the people who never got passed the tunnel level, I can see them not knowing or remembering those others.
Those people would get the Toads because "hey, I remember that game" and Dark Queen because she was the main villain (and also hot)
But that aside, Robo-Manus is the one I'm most looking forward to