Categorization does not cut it as a way of wading through a set of templates. Even if we supported nested categories (which we don't yet, see bug 150497) - there are too many conflicting critera one can apply, and one might not be interested in applying exactly those with which a category tree were created: * "Brightness" of document colors * Personal vs business * Module (i.e. is it for a drawing, spreadsheet, presentation etc.) * Copyright * Language/locale * Ornateness (this perhaps even a scale, but less say: High, medium, low, none) * Historical artistic current inspiration: Art Nuveau, Impressionism, Futurism, Dadaism etc (see https://artincontext.org/art-periods/) and possibly others. For this reason, I believe templates should be taggable, with the template manager being able to search/filter by tags. (A bikeshedding question would be whether users can tag/untag templates irrespective of the tags the author has chosen, and whether such tagging should affect anyone else.)
Bug 103319 regards another criterion: Presentation aspect ratio (4:3 vs 16:9 etc.). More generally, the target medium size is a criterion; for Writer documents, it would be things like US Legal, US Letter, A4, A5 etc. - and sometimes possibly several acceptable sizes.