That could be a longer conversation, but I think there's a subset of community-run projects that would be desperate for volunteers even if they were proprietary. In general most non-exploitative volunteer spaces are clamoring for volunteers even outside of software. Your local library is probably clamoring for volunteers (depending on the location). If you're in a rural area your school is probably clamoring for substitute teachers. And on and on.

I have opinions about the movement away from FOSS to source available licenses, but I think independent of all of that, smaller projects that fulfill important niches but that are not easily monetizable generally need help, and I don't think that would change if software licenses changed. Some projects could probably get better funding, but many would be in the same position.

I think in general there is more productive stuff to do in the world than there are people available to do it -- and I don't just mean in software, I mean everywhere. The world is held together by duck tape because a surprising small proportion of people volunteer to duck tape it together, and any effort that anyone expands towards helping them and making the world better instead of exclusively chasing whatever the next sexy high-visibility project is -- I think that's important, impactful work.