One of the things that has made this exchange so rewarding has been the focus on worldbuilding. I fear that this might shift if matching were done on pairings. As a writer, I want my concern to be on the worldbuilding tags my recip has requested, not trying to shoehorn in a romantic encounter. There are other exchanges for that.

So my vote is to stick to character matching.

If you are intrigued by the "eternal tag set" idea, the ToT mod asked for help from volunteers. Quite a few people did their bit to add past nominations to the set; and it might make the job easier for you.