1) Post-Avengers, Loki was tortured/controlled and Tony finds a bunch of wires and stuff embedded in Loki’s spine.
2) Loki is on Asgard to be executed and the Avengers are there. The execution possibly occurs in a gladiator-style arena (maybe with a tree) and is so horrific the Avengers convince Thor to help them bust Loki out.
3) Human AU modeled after The Lakehouse. Loki and Tony live in the same house but years apart. Tony may be a teacher and there is an explosion that may or may not kill him and Loki tries to stop it or something.
As always, thanks for your help!