The killer app in this space will be when someone figures out how to extract a vocal model from existing recordings of singers. Vocaloid already synthesizes singing quite well, but a human singer has to go into a studio and sing a long list of standard phrases to build the singer model. The next step will be to feed existing singing into a system that extracts a model usable for synthesis.
The RIAA is so going to hate this.
I understand it's hard but it also sounds like a fun project for people with the relevant know-how.
Reminds me of this article from 5 years ago: http://www.dansdata.com/gz103.htm
A cover band has to license the underlying composition, but not the recording they're covering. (This means ASCAP gets royalties, but the RIAA does not.) In the US, there's a compulsory license for compositions, and you can record and distribute any song by paying a relatively modest fee set by law.
This is just automating the cover band industry.
In ten years or less, this will be a common feature in DJ consoles, and we'll hear songs from musician A as if performed by musician B.
The RIAA is really going to hate that.