Now that hackage has caught up with ghc versions, I'd like my HaskellWiki project pages to link to hackage-based haddock docs instead of the docs I generate myself. (Hooray for inter-package doc links!) However, I don't know how to link to the latest version, rather than a specific one

This is not really an answer to your question, but rather a suggestion of a different policy. I think it would be useful to have links to the docs for each version. Not everyone wants or needs the latest.

You might also consider have a list or table with related links for each version, e.g. API, release announcement, and changes. IMHO, it's nice to have a perspective on the history of a project, not just the latest status.

Regards,
Sean