Selling out is working in a job that you do not like because you need to be able to pay your bills. I happen to like my job, but would jump at the chance to sell out as a full time musician. All this talk of "keeping it real etc" totally ignores the way the industry works. Massive Attack bloke writer retired from music a long time ago but makes money that the rest of us would cry about every year from people paying to use his music in this, that and the other.
Financially, the Video Game industry makes the Music industry look like children playing shop with plastic money and a till which goes "ching" every time it is opened.
Selling out as a musician? Make enough money from music to not have to work a day job and even (just imagine) fund a decent pension pot? Yes please.