As one of the official maintainers (the other one is Simon Hengel), I agree that Haddock can barely be called actively maintained and it has been like that for a long time now. It's sad, but we lack of time, which is the usual excuse of course. A more resourceful maintainer would be great, so if someone reading this is motivated and wants to help out, we'd love to be contacted by you.

I don't think a SoC project for Markdown support would be risky at all (with a sufficiently good student), however. And it wouldn't require a new backend, the backend would still be the existing HTML backend in Haddock.

David