Are there particular holes that seem obviously in need of filling that would be akin to "market failures" that could benefit especially from this funding model?

I always assumed there was a bunch of annoying unsexy work that volunteers wouldn't be drawn to and that could really benefit from explicit funding, e.g., something around automated testing and deployment, auditing, documentation, since most people hate that shit and do it reluctantly.

But that's just a guess. Anything jump out at you?

This ^^