An experienced software developer (someone that could reliably dig into an “SC4” scale project and not crash and burn) in a major city that isn’t SF/NYC/Seattle is something like ~70k in Europe / ~90k in USD (this is probably a little low as it doesn’t include e.g. health insurance, if you’re in a place where you have to pay for that). If you take that as rough baseline for “fair” pay (meaning full time developers aren’t implicitly “donating” money by working another job or living off of savings), then you could imagine 5000€/mo could basically pay for 2 half-time developers - or a 40k fundraiser might be able to get 2 full time developers for 4 months. This scale is not unrealistic for an open source project - Ardour, the open source DAW, has $13k/month in subscribers.
These numbers get easier if you think about the reach that SuperCollider has. For example, SC is a standard tool for teaching electronic music, synthesis, creative coding - the usage for this is VERY broad if you also take into account e.g. Tidal, SonicPi etc as well. These are classrooms full of students whose are likely paying >1k a semester for the course (either via government funding or private tuition), and learning with a tool that’s completely free. This is of course utopian and would never happen, but if you imagine universities agreed to donate $10/student/semester for SC classroom use, this would IMMEDIATELY pay for a few 1/2 time or maybe even full time developers more or less permanently. As far as I know, grants in the low tens-of-thousands for art+technology projects in wealthier European countries are absolutely available, and SC would be an easy case to make given that it’s open source, and enables thousands of artists and educators. You can imagine that one or two grants at this scale would “pay for” one or two large-scale SC enhancements (maybe not “SC4”, but some major steps along the way).
I think being successful with this requires some work - it took Ardour MANY years to get to the funding situation they have now. And, “one smart developer” is a very high-risk way to develop software - I would consider it almost a no-go - so finding a way to properly support a “team” of some kind, while still compensating them fairly is an interesting challenge.