Conventional font categories are practically useless to me. Almost every font I make falls under decorative, sans-serif or both. That's not much of a category range. Pretty much anything before Morrison I throw into the Ancient category. I don't have any need to subdivide that category. For my purposes, those fonts have a common thread: not particularly interested. Most if not all font categories deal with pre-Morrison archetypes.
Old sans (Franklin Gothic and other sans with ancient flav)
Geo-classical (Futura, Gill, Bernhard Gothic)
Helveticas (Arial, and hundreds of other mid-century neutrals)
Frutigers (Museo Sans, Verdana)
Humanist sans (Easy. If the baseline is straight, it ain't humanist. Most of what I see categorized as humanist are just Franklins.)
Geo-gothic (Avant Garde)
Square Sans (EF Digital, Bank Gothic, Chimes)
Superelliptical (Microgramma, Eurostile)
Brush Sans (Flash, Balloon)
Techincal (DIN, Highway Gothic, stencils, elevator buttons, template lettering, labels & other "ugly" lettering)
Pixel (early computing retro, including segmented LED)
MICR (Data 70)
Rounded Sans (V.A.G., Arial Rounded)
Compacta (Impact, Helv Inserat)
Industrial slabs (Memphis, Museo)
Stops (Stop and similar minimalist variants produced in the 70's & 80's. I didn't think it was a category until I moved to Japan. Bored font historians looking for a subject should try tracking Stop's influence on car emblems, videogames, graffiti and the circa 1990 4k demo scene.)
Geo slabs (Lubalin Graph)
Structured scripts (Magneto, Deftone Stylus)
Decorative (Actually decorative. Fonts that look like fire or chrome etc. It's often used as a catch-all category by the ancient ones)
Misc (a better name for a catch-all category)
These are the categories I use in my work. Unfortunately, other people don't see these as categories. A famous font grump called my Pirulen font a Bank Gothic knock-off or something but he probably wouldn't call every transitional font a Times knock-off. Categories are important. Exploring a category sounds better than knocking off.
In the future, people and machines will make more Geoslabs. They will all resemble Avant Garde Gothic a bit. Geometry, baby. People will make Compactas that look somewhat like Compacta. They'll make hundreds more MICR and Stop inspired fonts and there will always be those who will place them in the Decorative category and call them knock-offs while they toil away on the next great, slightly-different Garamond.