I consider myself a casual/hardcore (somewhere in the middle) Nintendo fan; I purchase most of the triple-a titles, I am current on most news, I own a Wii U/3DS. I have supported every one of their consoles... and I have no idea what Rhythm Heaven is.
Well, my friend, you would do yourself a massive favor if you tried out either the DS or Wii version of the game. Super easy to get in to, super fun to play, challenging, and hilarious. Seriously, there was a stage I played that had me laughing so hard I couldn't finish it and had to start over.
Which is why this pick is not a good idea to me. Even with casuals there is literally nothing there. Nothing there for Sakurai to make his own like with Pit, nothing there history wise. Just a niche supplement game and franchise. I mean what the hell is the trophy going to say? He wasn't even the main character in most of the games and Marshal was the only one important. And their names are Choir Kids technically. This is a damn nightmare so its probably true.
I dunno about that. Given the completely random nature and massive selection of minigames the full games provide, I'd say there's a ton of source material to create a moveset from. Much like how Mr. Game & Watch derived his moves from each separate Game & Watch handheld game, Marshal could take each move from a particular mini game in Rhythm Heaven. He's got fireworks, balloons, monkeys, badminton, space robots, pigs, moai statues, bacteria, love potions, dogs, guitars, candy, spiders, TONS of material, and that's just off the top of my head.