Sorry to bump an old thread but I agree with the OP that tags in packages would be very helpful, and I can think of at least one use case in which they might be necessary: games.
While game genre can be put into the description, games right now are not all in the same .scm files (for example, gnome-mines is in gnome.scm and not in games.scm). I've checked out all descriptions and so far you've done a good job of incorporating game genres into descriptions, but there are some cases in which that is not enough. For example, if I search for "board game" then a game like gnubg won't show up, because only "board" is in its description...but searching for "board" alone might bring unrelated results like non-board games that have boards in their description (like Five or More from GNOME, a puzzle game) or unrelated software like kanban boards. Also, in other package managers, people are not consistent in their descriptions and so "RPG" and "role-playing game" and "role playing game" can all give different results. I think this issue should be solved by approving each tag, so that they are used carefully (the same could be said about descriptions right now, but it'd be harder to enforce). In short, I think tags are a simple solution to a problem that's been around for many years, and the fact that it wasn't done properly in the past is purely anecdotal and doesn't mean it can't be done properly now. Filtering is a very important issue, IMO, and tags are pretty much the only solution to facilitate it (since categories can be too broad - VLC and Yoshimi are both audio programs, even if they are completely different). I propose that tags are implemented, and that each tag has to be approved by the devs before it is used, and that a list of all tags is published on the Guix website to help people choose the right tags.
