I'm glad the shared ownership thing is working out for some of y'all, but it's not a situation I'd be up for. Why would I, as a band member, want to own ONLY the board? Or ONE P.A cabinet? That doesn't make sense for either me or the band.
If I leave the band and the rest of the group can't or won't buy me out, I take whatever piece(s) of the P.A. that I "own" with me. At which point the band is left with an incomplete P.A., and I'm stuck with gear that is useless apart from the rest of the system. So then I either have to sit on it until I land with another band (who may not want or need it), or go through the hassle of selling it.
It's true that when everyone has a stake in the P.A. it does provide a very strong incentive for everyone to make the band work long-term vs. somebody bailing at the first minor annoyance so I can see some merit in that.