Some US musicians may soon be able to reclaim copyrights from their labels

There's no reason the individual artists can't sign up with ASCAP, BMI, Harry Fox, etc. (or some new similar agency) and I would expect most of them to do that (many already have, of course). The exception would be, as you say, the very biggest artists. Most small to mid-level artists aren't going to want to hassle with (or pay for) individual negotiation any more than the your music startup will.

Ever tried negotiating with a major label? If you had, I suspect you might change your tune. Furthermore, musicians are far more likely to agree to reasonable terms, as their organizations are far smaller and less byzantine than a major label.

For the record, I think this is a great idea. The major labels have been operating with a plantation mentality; now they're getting their version of the Emancipation Proclamation.