I think it's a safe assumption it will. It's a somewhat popular and decently selling franchise with a pretty solid following to boot. (Especially in Japan) I'll even go ahead and say It's not a matter of if we're getting a Rhythm Heaven game for the Switch, but rather when will we get one?
Though I can't see it coming in the near future. Sakamoto is currently working on the Metroid series and who knows what Tsunku is up to (Probably still recovering from his health issues a few years back and working on other projects.).
As for how it'll be like, I imagine it'll be like most Rhythm Heaven games beforehand, nothing too drastically different from past titles. (Who knows though? I've been surprised before.) Though I can definitely see them wanting to utlize the joycons' capabilities in some fashion. (I can see them using HD Rumble as a beat during the games.)