My band recently instituted something like this. Since we were having trouble with resentment over certain members contributing more time or money than others, we started a "share" system. Each "share" gets you a share of future profits. We had a lot of discussion about whether we would let outsiders buy into this system, but ultimately decided yes with the caveat that shares do not equal voting power. So far we haven't had anyone outside the band want to buy in, but it has solved some major problems for my band. In addition to to curbing the resentment factor, we now are buying band equipment, have built a drum riser, working on more stage elements, and an upgraded merch display.
I think it would be awesome to get some angels or something like that to invest in a RBF. However, we're still so new that we haven't reached full sustainability quite yet.