Yeah, not too much vocal songs, but a few at some points would be really great.
Transistor made it perfectly as i think.
https://www.youtube.com/watch?v=cGMWL8cOeAUIn Transistor there are 4-5 Vocal songs which fit in the Situation Red is, and the other music is also great but non vocal ambient.
Really would like to see more of this great Vocal music in Games.
Of course it is difficult to make, but in my opinion would be no waste of time.