OK, there are a few fanfic stories I’d really like to read. Perhaps I’ll get to writing one someday; more likely not.
Two alternate versions of Harry Turtledove’s Lizards/Worldwar books:
1) “Fleetlord Atvar and the Cuban Missile Crisis”
2) Lizards arrive in 2021, as described/implied in John Birmingham’s Axis of Time Trilogy
1) Book 7 ends with Harry and Voldemort, the way Ralph Bakshi’s Wizards ended
2) An alternate universe where Harry joined Slytherin house
There are some others I’m forgetting now, perhaps I’ll update this later