> It seems like `read-from-minibuffer' doesn't like having its HIST
> parameter be buffer-local (but I may have misunderstood the problem).
> I'm going to look into it more on depth these days.

Here's my first attempt at implementing this - I managed to get around
the `read-from-minibuffer' problem with some help from the Emacs
StackOverflow (but created a separate bug report for it:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38317). I'm attaching a
small patch.