I recommend getting this in the App Store so musicians can start using this. Even for a very simple version, charge at least $1.99.[1] Don't over engineer it in terms of features within the app, but make sure the core functionality works as advertised for a broad range of folks. There is a massive novelty factor here which I think will create a viral growth of sales. This will allow people who can't beatbox to experience the joy of beatboxing. :-)

If it continues to works as advertised as it evolves, I think you could quite easily find yourself either in a licensing agreement (or small acquisition) with Apple. Their Garageband app is packed full of "smart instruments" that are in a very similar vein as this. Most of them are quite awesome. My son is obsessed with playing them. They allow even kids to have fun making music and experimenting with sound. Something like this would be a real improvement from what they currently do for "smart" drums.

So, I think there is an initial awesomeness which is that you could have a successful app, which in itself would be a real accomplishment these days. This concept definitely has the potential. However, I really, really hope to see this picked up and incorporated into a larger tool for creating music in a fun way.

Best of luck, guys. Great job.

[1] Might be a bit specific in terms of advice, but not knowing your background/experience building and marketing apps, I thought I'd throw it out there. Coming in with a price tag that's at least $1.99 gives you flexibility with promotions, etc. down the road. Furthermore, something like this definitely provides at least that much value/entertainment.