The idea of pairing tags has been floated in shadowy backrooms before, and I (as one person, who doesn't have final say) am perfectly open to the idea. I'm not convinced we would need to pick one pairing tag per character, and that seems needlessly limiting given the series' variety. Ideally, the tags would follow exactly what content is depicted. So that should be a non-issue. However, I'm just a casual reader here, so I could be totally wrong on all of this.
I didn't actually consider that. I can see how that could work out, if the person who assigns those tags doesn't have their goggles on too tight and actually wants to go through every chapter to judge which pairings are even to be considered and if they're represented strongly enough in each chapter. For example, I don't think a Kaname x Yatsude tag is even an option even though Kaname keeps hinting at having an interest in her, which Ningiyau even confirmed in an interview.
I just want to err on the side of caution and not give readers wrong expectations when they see the chapter list for the first time. So as long as they're carefully applied based on the chapters' contents and not a staff member's preference for one ship over another, I wouldn't actually have a problem with that kind of pairing tags.