After sufficient complaining ensued on Reddit after my previous blog post, and enough claims of "this is so trivial to implement," I decided to bite the bullet and just implement it. After debugging a lens bash script, I reimplemented it in pure Haskell and added it to my mega repo tool chain to be part of my normal release process.
So for everyone who thinks that Hackage is the right place to have documentation: it's there again. I'm still quite unsatisfied with the whole situation, and have wasted yet another hour of my life on what in my mind is meaningless busywork. But so be it, it's frankly easier to solve a technical problem than put up with the complaints. (I've certainly spent more than an hour in the past four years explaining to people multiple times why docs on Hackage don't exist for my packages.)
Now I'll put out a request: will someone please implement READMEs on Hackage? Yes, I could do this, but I've never touched the code base, and have lots of other things to do. The current situation of having to describe our packages at least three times (synopsis, description, and README) is annoying, and the fact that some forms of documentation cannot be expressed at all in description fields is very problematic (see linked mailing list thread in that issue).
I hope I haven't just set a precedent that complaining at me gets me to do work I don't like...