Yup.

And more generally, setting aside morality and the free-riding economic issues: if the open source peeps are producing something that "we" really care about and value -- in this case, a vibrant btc dev scene -- then what can "we" do, what structures to adopt or build, that could support it?

You owe nothing. If the project is proper FOSS and there is demand for it, someone will pick up the mantle and continue or fork.