It does not work with recent versions of Postgres, it segfaults in some cases, and it has been mostly abandoned. Otherwise, it would be (and it has been) a great way to develop FDWs.
Yup, if someone picks up maintenance again then that can continue. But if that doesn't happen, we really need to stop mentioning/recommending it. I see it all over the damn internet, well after it became unmaintained.