There's no universal standard. Judging by discussions we've had here before, people can't even agree on what constitutes "kink", let alone which ones are fair to write unprompted and which aren't. Some exchanges (mostly flash exchanges, AFAIK) have official opt-in lists that include certain kinks, but Yuletide doesn't.
Generally speaking, IMO, your best bet is going to be to prompt for what you want, and/or have a likes list including some smut likes to draw from, DNW what would absolutely 100% ruin a gift for you, and let a presumption of good faith take care of the rest. On the one hand, most people are not likely to write you an exceptionally kinky PWP totally unprompted; on the other hand, if you're asking for an m/m pairing with an age gap that's got a lot of daddy kink in the tag, you should probably let your author know you want them to avoid that in your gift.
Re: Kinks that are opt in/opt out
Generally speaking, IMO, your best bet is going to be to prompt for what you want, and/or have a likes list including some smut likes to draw from, DNW what would absolutely 100% ruin a gift for you, and let a presumption of good faith take care of the rest. On the one hand, most people are not likely to write you an exceptionally kinky PWP totally unprompted; on the other hand, if you're asking for an m/m pairing with an age gap that's got a lot of daddy kink in the tag, you should probably let your author know you want them to avoid that in your gift.