In which format should GHC expose documentation via its .hi-files?

Hi! In preparation for the coding phase of the Hi Haddock proposal that I want to implement, I need a decision on the format in which we should expose haddocks in GHC's .hi interface files. Please visit https://github.com/haskell/haddock/issues/805, ask questions, make suggestions and help me find a timely decision! :) Cheers, Simon