It'd be more of a oneshot I think. You might could wring a few chapters out of it though.

Harry Potter dies at some point. Triwizard Tournament if you want to have the entire school involved. (Maybe his family is still alive. Maybe not.) Late stages of the war if you only want the order of the phoenix. All hope is lost, and in comes Albus Dumbledore with the solution to everyone's problems. He sells everyone on some arcane ritual to summon a version of THE CHILD OF PHOPHECY that has already completed his task. Everyone is channeling their magic into the ritual and when everything reaches a fever pitch then POOF, giant white smoke cloud. As it disperses you see a thirty year old Naruto and his wife femaleSasuke. Since they're Asura/Indra it kind of makes sense. Maybe Sasuke didn't leave with the snake guy and they persevered through all the complications involved with saving the world. They've essentially been relaxing the past few years and letting the next generation take over. Naruto was Hokage for a few years before he got irritated with the whole thing and trained a successor. Oooh, and I've always imagined the scene going something like they're sitting on the couch reading. Naruto has a pipe in his mouth visa vi Saratobi. femaleSasuke is leaned up against him with a book. Wormhole opens beneath them and sucks them through despite them struggling to get free. There's an "Oh shit" moment like "Goddammit, idiot. I've only ever had shit like this happen when you're around." Dumbledore tries to bind them to their purpose only for Naruto to flare the fox chakra and eat through every enchantment in the room. Moment of awkward silence. And then whatever from there on in. Maybe they agree to help for mountains of gold. Maybe they Flying Thunder God away. Anyways, I've had that one scene where the smoke clears and a 6'3'' Naruto is just sitting there swirling around my brain forever. It's probably pretty shitty, but idk. I think it sounds pretty cool even if there's nothing in the HP universe that could be considered anywhere near the same power level just based on how fast the ninjas are. Maybe wards might be an issue.