That's an unexpected, even though it seems harmless I didn't know what that thing is capable of. It's better to be cautious even if it's an imaginary thing. :/
If I were a teenager this might be interesting, but for most of older people on MD (including me) I found this a little bit annoying. It's only applicable for people who reads or following popular shounen manga, and I can see it would only become spam quickly.
I don't think it would benefits to most of user because usually the demographic has already covers the need for this kind of thing. As for the worst case it would only make more confusing tags. I have already seen this implemented on Mangaupdates and even then it's not very effective.
Since when slavery become prevalent in harem manga? Even though I've read a lot of isekai harem or generic harem, slavery as a thing isn't something that I encountered very often. It's very niche thing, and in my personal opinion isn't something that need to be added as a new tag.
Slow pace romance in this story is better than the most of the Isekai that have exist currently, I'm tired of the fast paced romance that are common on today's Isekai. 😄😄😄