I was in older op forums as well long back
Some of the theories were wild i remember:
1. Sanji was Gorosei's son theory
2.Big mom -lola theories and big mom would ally with luffy after finding out luffy rescued her.
3. Sabo is Gladius theory , doflamingo offered him crew spot to avenge luffy for Ace's death.
4. Bobbin was a sweet commander. I remember a former user who was huge bobbin fan made some crazy theories.
5. Monet is alive theory
6.Law was son of doflamingo theories were wild too because of similar jolly roger .
7.Xdrake was secretly marine -This one got real
8. Zoro is son of shogun and he was lost son .