I think pairing tags themselves such as enemies to lovers get into the weeds of subjectivity too much to be useful. How long does someone have to be an enemy to constitute a romantic relationship with them as a enemy-to-lover? Is Sasuke/Naruto enemies to lovers because they fought one time? (I've never seen Naruto. I'm being disingenuous like any other user browsing the site might be.) And actually typing that reminded me, how would people who've never seen the copyright and just dump all art of X gender configuration apply this? It'd have to be gardened in by one or two people who love it, which is subject to abuse.
And finally, something like post #11378459 where the pairing itself does not make any sort of sense could also work as a tag imo. Basically completely nonsensical shipping. Maybe nonsensical relationship? nonsensical couple, nonsensical pairing?
This one I agree with. What about anachronistic relationship? To go with anachronism.