I'm a big Rhythm Heaven fan and at this point I'd be disappointed if the series gets anyone other than the Kids. They have so much potential and legitimately represent the series better than any other choice. And ironically, it's the idea of the Kids that got me back into Rhythm Heaven. So it's in reverse: I liked Chorus Kids, and started playing RH again.
Sure, CKs were not vocally desired. Neither was Wii Fit Trainer, but many of us love the idea and are happy that she was included. Vocal support isn't always necessary for a character's inclusion: it can be what they bring to the table and how unique they can be as well. Of course, a character needs merit too. A character has to deserve their spot.
Chorus Kids are a great choice for a variety of reasons. First off, they are music based. Rhythm Heaven is all about music; the whole game revolves around it! So it makes sense for the representatives of Rhythm Heaven to relate to music: hence, singers. Also, they're a trio. It may sound a little weird at first, but I'll explain. Many minigames in the RH franchise revolve around a group of near identical creatures, keeping time with each other and mimicking each other's actions. Chorus Kids' whole playstyle would revolve around this, so not only are they representing Glee Club, but a variety of other minigames as well. Also, being a trio arguably makes it easier for some rhythm based mechanics to work. In addition, Chorus Kids are quite possibly the most marketable characters in RH. They're pretty memetic, spawning videos of other characters singing along or the Kids themselves singing other things. They appear front and center on the RH cover art, have been used for standees and promotional comics, and even made a cameo appearance in Game & Wario. So they're recognizable, and the creators of Rhythm Heaven clearly love them.
They don't steal G&W's mechanic, either. They are 2D, but they look like Ed Edd n Eddy styled sketches, with wiggly lines and simple designs. G&W is flat, but moves frame by frame like a G&W sprite. Chorus Kids wouldn't steal anyone unique from Mr. G&W, and I don't see why Monkey, Wrestler, and Girl would be any different. If anything, they don't have that sketch look, and would have less diversity than the Kids. I don't agree with this, but if you're going to claim that they steal G&W's shtick then that's what I'll rebut with.
They're just a great choice in my eyes. I saw the leak and said "nah, it can't be possible". Then I started to think about it and play Rhythm Heaven again, I got excited about the idea, made the thread, and here I am, possibly the most vocal supporter there is.
The leak is the reason I support them. But not for the reason you think. Without the leak, I never would have thought of the idea. But thanks to Sal, I started thinking about the possibility and I think it's excellent.