Formalizing it does break Yuletide for people who are neutral on gen vs. shipfic though. Instead of nominating and requesting A and B and calling it a day, they'd need to pick either A/B or A&B (since AND matching means you can't pick two mutually exclusive options), and conceivably the mods would have to adjudicate what counts as shippy enough to qualify as A/B. And what if you want A, B and C, and A and B can be a couple or A, B and C can be a threesome or it can be gen depending on your writer's preferences? Something like that used to be very simple to request for Yuletide, but under AND ship matching it's impossible.
It's also going to complicate matching, because if you've got a fandom with twenty characters and you're not willing to offer any, you used to be able to offer 10 characters and match to any combination of them, but now you can only offer them in various permutations. What if someone just offers A&B but I requested A/B? Now I'm unmatchable, whereas under the current Yuletide system we would have matched, and they might be perfectly happy to write me the shipfic. For people who exclusively want to receive or write shipfic or exclusively want to receive or write gen ship matching is preferable because it eliminates the possibility of an id mismatch, but for everyone else it creates problems.
Adding worldbuilding, OTOH, only affects people who choose to request or offer worldbuilding. It won't interfere with people who want to do character matching at all, except possibly by taking some people who don't really want to write 'Any' out of the offer pool. It's like if you could implement ship matching only for the exclusive shipfic and gen requesters/writers without fucking character matching up for the rest of us - if that were possible I'd be in favor of Yuletide adopting ship matching too!
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It's also going to complicate matching, because if you've got a fandom with twenty characters and you're not willing to offer any, you used to be able to offer 10 characters and match to any combination of them, but now you can only offer them in various permutations. What if someone just offers A&B but I requested A/B? Now I'm unmatchable, whereas under the current Yuletide system we would have matched, and they might be perfectly happy to write me the shipfic. For people who exclusively want to receive or write shipfic or exclusively want to receive or write gen ship matching is preferable because it eliminates the possibility of an id mismatch, but for everyone else it creates problems.
Adding worldbuilding, OTOH, only affects people who choose to request or offer worldbuilding. It won't interfere with people who want to do character matching at all, except possibly by taking some people who don't really want to write 'Any' out of the offer pool. It's like if you could implement ship matching only for the exclusive shipfic and gen requesters/writers without fucking character matching up for the rest of us - if that were possible I'd be in favor of Yuletide adopting ship matching too!