The one I think are prevalent / different enough to have a tag
-childcare, that one is pretty obvious with all the """vilainess""" step mother webtoon alone
-idols, pretty surprised this one is not there but ig idols is more prevalent on the anime scene
-"1 to 4 pages / Twitter" they are very prevalent and the flow of those story (when they have one) is very different than a story that allow them self to have more space per "chapter"
Now for some "nice" to have
-journey / "world seeing" for the story where the world is it's own character and has a focus, could be a "made in abyss" or "dungeon meshi" to cite some popular but quite a lot would fall into
-economy is a niche but i do not think people would mind to have it
-motorsports same as economy from the top of my head I can think of some without ever reading anything more than initial d
-female/male protagonists, again often written differently and sometimes you want to find one instead of the other, also would eliminate the tag reverse harem as you could chose FL + harem instead and we already have the shota/loli tag for what it is worth, I will leave the discussion about the specific term of "female/women male/man as I am not a native speaker of English (in my language the former is kinda sketch to use but I have no idea about the EN community)
-tower / dungeon, I do not read story about the ever more popular koreen tower / hunter trope so correct me if I am wrong but they may deserve their own tag at this point, dungeon crawler may be wider but still validé tag
-western/eastern esthetics, self explanatory, like if you go eastern + history + military you get kingdom and western + video game you get a lot of isekai
-fashion I do not know if this is prevalent enough to have a tag but I am throwing it in
-possession a lot of isekai vilainess end up being possession, some people may be tired of reading possession story that never addresses the problems with taking control of someone body and would enjoy being able to filter them out of the vilainess tag... (yes I am talking for myself loll
Extention / change of some tags
-video game should be extended to more than being isekai in a world that is expressly said to be of a VG to any story where floating windows, xp, skill point or stuff like that exist, they have a very different way to handle character progression. Like wuxia cultivation is pretty different than more organic progression. Now I am aware that those element did come from tabletop game first but I think the tag name is not a problem
-Loli / Shota tag is probably more "charged" than necessary, like yaoi can be, we changed Yuri and Yaoi to the less charged girl's/boy's love and people can chose the level of spices they want with the content rating, so I propose the tag "Kids", what made me think of that was seeing ascendance of a bookworm part 2 being tagged lol I but not part 1 or 3, some team fear to put the tag as some people have strong feeling about the "Loli/Shota" tag when nobody would have tough twice about tagging them "Kids"
Their is a lot of other than I can think of or change / merge in the "theme" section but I do not know if the mangadex staff is trying keep the tag under a certain number or not
Also my keyboard is dead and typing on mobile is kinda a pain (sorry for not hyperlink to the Manga named)
Brutal. 
