This is the same economic problem that affects basic research. Open source software is a 'public good' - its usefulness is not diminished when it is used by others, and you can't prevent others from using it.
The longstanding solution to this problem is government support. This might not be a sexy solution on HN, but it is the obvious one.
Unfortunately, while government can mostly wrap its head around science though consultation with academia, the state of the art of software is so ethereal and moves so fast that I imagine seeking funding for software will be even more of a farce than it is in the sciences.
Incidentally, Snowdrift.coop is happy to have projects doing scientific research. The basic criteria are that 1) the project is producing some non-rival good, and 2) that good will be made freely available under an appropriate license (which basically boils down to the equivalent of one of CC0, CC-BY, or CC-BY-SA).
Government support works when you can get a majority of the people to agree they want something enough to pay for it. It works less well when the public good primarily serves the interest of a minority. In principle, even if government support was effectively tackling all the things it was appropriate for, there could be room for Snowdrift.coop in coordinating more niche things.
I agree it would make sense, but is the real problem not how to allocate that money?
Who decides how much the Postgres guys get, or if its worth to support yet another NoSQL store? Involving politics seems like a surefire way into mediocrity. How to get around that?
Maybe the government could provide the funding as a Tax Credit for donations to platforms like snowdrift.coop, just like donating to other non-profits works. Companies / Individuals would make their own decisions about what to support, and the government would foot the bill through them.
Obviously the government would create a class of acceptable organizations to donate too, rather than designating a single platform / portal. In this way it would be just like the new crowd equity system.
The longstanding solution to this problem is government support. This might not be a sexy solution on HN, but it is the obvious one.