So there's the not so crazy one that I've been going for for some time now, which is the "TFP is John's TAB" thoery, but I will admit that there has been two others that have been on my mind.
This one here https://the-7-percent-solution.tumblr.com/post/163693520958/his-mind-created-the-perfect-metaphor provides a lot of ample sense to one of them, which revolves around the "What if Sherlock actually died" thoery. And is actually not that farfetched.
The other one I've been pondering about would be the "What if John really went mad" thoery. Basically, it entells that the entire show is fake. That Sherlock Holmes doesn't actually exist. That it's all really an elaborately detailed life John has given himself in his own mind from the very start, whether he killed himself in ASIP or not. Think about it. John was at his lowest, and all of a sudden he's swept off his feet and his life is forever changed? The whole plot of Sherlock is over romanticised. And honestly, it's unrealistic and too