award important fixes aren't making it in as quickly as they could
Then I'd say that your idea of important and the core developers' don't jibe. In fact, if people are moving on with their lives and leaving PRs behind, they must not think the PR is very important either.
The normal way to fix this would be to get a lot of volunteers to do the bug catching, formal testing, responding to new issues, and documentation that bogs down development, so the project leaders could focus on checking pull requests. Of course since this is all volunteer work, that method assumes that the project leaders enjoy checking other people's work and won't be distracted by more interesting work of their own. 🙂
Or, if you're really ambitious, you could fork the whole tree and approve pull requests yourself. Document the whole process heavily so that the project leaders can follow it easily. Then get a lot of people to test it, to show that they really do work. You could call it the warp-speed project, or some such.
