Ohhh that is a very good idea. +1 on the teaching angle already mentioned
Don't care if Activision is cancelling guitar hero. The reason why that was so popular is because people like music. I mean MP3's are still popular. Then people love video games. And when you combine video games with YOUR favorite MP3's, its an insta hit.
But like most video games its fun, but it doesn't teach you anything. The video gamer crowd is never satisfied; this years game of the year is old news 6 mo's from release, unless you get rare games like IL-2 sturmovik (2001 release and fans flock the online servers still). And also Guitar Hero "rockers" are considered weaksauce, so once the novelty got old, then it got old because unless you played for real, you weren't cool as the real players, you were just a poser. Google that microsoft / bill gates / slash video with that guitar hero champion girl, and people clowned her when compared to slash.
But if its a system that teaches you how to play bass or be a better player, then, you got something. With the ability to jam with songs you want, bands you want, that is a b00n to players. Especially the non gigging / bedroom player crowd.
However if you market this to the bass player / guitar player segment (I highly / strongly advise you include guitar in), then you get something fun.
I find that I have to push myself when I lose interest in learning bass / guitar because the beginning songs really isn't something that I can get into.
But I found out if I play my songs on a tinny logitech speaker on my PC, its fun to "play" the bass along with it.
They have tuners that tell clip on and even though its super loud, you can tune your guitar around. I know, where have you been Min? Those came out x years ago . . . So get a uber one that can detect notes on the fly, or chords etc. Make it wireless, and it transmits to the game system . . . . Clip it to any bass headstock . . . people can learn to play better on their weapon of choice.
Or people just plug their bass into the game system, and viola, it detects what you do on your bass and the game determines if you get close or not . . .
You could also do the video game aspect of a story adventure, because that draws people in. Include something that can involve people from different walks of life . . . Like have a whole customization character screen. People can be that old blues player who's everyone ripped stuff off to that neophyte, wide eyed teenager with the whole world ahead of them . . . or the hard rocker going to show the kids how its really done etc . . .
have you, the player, be the hero or bad a***, in really great storyline. Or just have an arcade mode where you can play with a band or solo, or select what instruments you want to play. If you have a good story, people want to get involved, and be a part of it. Look at how mmo-rpg's or rpg video games they have a great following, without serious action you'd find on Call of Duty MW 2 . . . Choose yer own adventure books still are popular (though I think its now flash based n online
Maybe mix it up like have you be bass for different music genres etc . . . and have a n00b, medium, advanced, expert, and maestro version . ..
Then you could have a lutheir's corner, like how Forza for the PC draws in all the car enthusiasts because they can race and mod their fav cars. They have real life cars in there.
People can mod their basses / guits, and there is a selection of tonewoods, pickups, amps etc . . . has realistic sounds, and people can make a guitar or bass, then test play it (instead of their bass tone coming through, it uses the games for that type).
Oh and include bass greats, like Crossroads, you vs the devil's chosen bass player, and then plot twist and you get saved by Jaco!
Another thing to consider is the social / online thing. Maybe do a SIMs like situation where players around the world can chill, play, talk shop, teach . . . heck even get certain brands, luthiers, players in on it, like Gran Turismo has Japanese car manufacturers . . . Thats a strong area . . . heck even a discreet advertisement here and there would help cover bandwidth / hosting costs
Ok I'm rambling, but just being able to jam with your fav bands and favorite music. Awwweee sooome!