I think the approach should probably move towards semi-tailored systems.

Maybe you don't need all of Postgres - so provide 2,3,4,5,n versions. As long as every version is covered by (possibly shared) tests, then you can release what works, ignore the rest (bugs and all).

Exactly. And over time a project can drift from its original purpose, so you end up building around a bunch of stuff you aren't using anyway, but you pay cost/risk for having it present.