Kinda like what you said. I think he'd basically "cue up" certain moves to be given another input, which'd allow them grow probably stronger?
That had me then think: what if Chorus Kids' attacks would be "extendable" via button inputs, in style of Meta Knight's F-Tilt and and Bayonetta's F-Tilt and F-Air, and then allow the timing of inputs together he dictate the move's power... which'd allow some interesting conversion of RH-series' usual gameplay?
My set up would be that you'd be defaulted to one Kid only running around in general (Marshall?) - or maybe the two others trail behind him all the time, but then go disappear behind his back. RH-chars had been shown to be probably similar paper-thin characters as Mr.Game & Watch is, if looking at the RH-trophies we saw in Sm4sh Wii U.
On that end, I personally though feel three kids running huddle together would make them too big and easy target due perceived big hitbox, hence why I think it'd be better for them to just be allowing one be visible and let other two come in for attacks.
When performing the attacks, usually it'd be a swift move from the first Boy - and you can extent the move further with more inputs. However, together the blows are usually weaker, or the sizes of sourspots are bigger.
But if you press them to the right "timing", another Boy would zip in from first one's back to swiftly extent in another blow - do another well-timed input after, and 3rd one would come either for one more hit, or a devastating finisher. Maybe there's a 4th one that has them all three hit together to really bring the opponent down the building.
But how to tell when is the right input or not?
That's where the
Conductor comes in. He'd be in backgrounds of any stage, and through the way he would wave his cue baton to what's right "time" to do an input, you'd see when to hit it or not.
With this, you can also alternate between weak attacks and strong attacks, allowing potential for combo strings, while giving you good sense when there's a "miss" input and "right" input: much like Rhythm Heaven-games.
On that end, good sum of these "missed inputs" could create "mishap" attacks, sorta like having the Boys mess up a move in a way that happens to hit their opponent nearby, styling after that tongue-in-cheek humor you see in RH-games when you miss a right input.
Probably might go dig through the games for fitting examples.
Heck, I could see this extended to Special Moves as well that would have the characters do them as you see in RH's various games, and you're allowed to "miss" the input to an alternative move in some, though others might require to really input the move well for maximized effect.
Overall, I think Chorus Kids might hopefully be one of the currently increasing "technical" characters you'd play in Smash, along with deploying the "triple power" concept on to them. I hope there's something like that in the works, in case they seem to all ready and feasible after Sm4sh had cut the Kids out.