1) Druidism or something Druidic based becomes a major faith.
2) The war of Confederate Independence seen through the eyes of Cleburne! The Musical. Or alternatively the otl American civil war through the eyes of an alt version of the same musical.
It has a lot of asides about the evolution of artistic trends in the Confederacy. But basically alt history of Jazz, Rock, Country and Folk, rather their alt historical equivalents.
3) ATL The 1976 Winter Olympics in Denver and the 1936 Summer Olympics in Barcelona. Similarly I'd like to write about South Vietnam winning its only Olympic medal, a gold, in Montreal, on the day of or after or before the country ceases to exist.
4) The Saga of Raund the Strong. OTL he bravely died fighting Olaf Tryggvason. ATL he defeats Tryggvason. ASB version he dies and then leads an army out of Valhalla against him.
5) One of the American Founding Fathers is captured and raised by Indians or by the French Canadians. I approve of kidnapping fictional small children and raising them in different circumstances generally. I wish Indian style kidnapping and adoption were more common across cultures.
One person/people who would be fun to do this to is have Guthrum raise Alfred the Great's kids and his daughter Athelflead in particular in a Norse pagan setting.
6) A tl where psychology arises in a culture where hallucigens, vision quests, and shamanically induced altered states are mainstream practices and become scientifically documented treatment methods.
Edit: added the Alfred/Guthrum bit and the 1976 Montreal bit.