I feel like Snape's backstory would be really cool. We don't really get to see much and maybe it'll give more depth to the character.

I really like Sirius and Regulus so the blacks

The four founders or the black family

Tom Riddle

Marauders

A lot of people want a marauders one

First wizarding war. In other words, the other two Fantastic Beasts movies they were supposed to make!

The marauders