When you say make the "crossover/fusion detail required" do you mean that it could be a selection in the offers, too, and people can match on it? If so, YES! I have never been able to participate in this exchange because I have no interest in reading or writing AUs (which fusions are). Especially since requests were not visible during sign-ups last year, there was no way to avoid matching to someone who wants only fusions (or vice versa, for the many people who hate crossovers). I think you'd get more participants if you made it a matching factor; I see just as many AU DNWs in exchange letters as I see prompts for them. People who like both would be unaffected, because they could select both.

I like matching on fandom-only (as you've had it in the past). However, if crossovers/fusions isn't a matching parameter, then I'd selfishly be all for relationship matching, as that seems would make this a crossover-only exchange.

Long story short, my answers to the poll questions are interdependent so I'm not sure how to answer.