> Speaking of 'f' and 'q', do we have a precedent for this kind of
> interaction somewhere else in Emacs? I'm not against those per se, but I'd
> really rather we try to follow one of the existing workflows, so that the
> users wouldn't have to remember yet one more thing. Hence the idea from
> package.el.

I see no reason to be different from package-menu-filter where
'/ /' resets all filters.  Then maybe add '/ i' to include, and
'/ e' to exclude.