I've never really read fan theories until now. I must say, some of them are quite interesting and are quite realistic. There are a lot of ideas about what may happen on Wano/with Kaido and such that sound accurate.
Have you read any of the Scopper Gabban theories? Interesting stuff. People think he was the guy talking to Crocus in the one title page dressed up in Wano clothes, so they think he'll pop up soon and do something noteworthy.