9 Ways The Simpsons Could End

Why does everyone in Springfield (except God, of course) have four fingers? Why are Bart and Lisa still in the same grade after twenty-eight years have passed? How exactly does the Armin Tamzarian actually work?

The simple answer is, of course, a wizard did it (or it's just a cartoon that's ran on for a long time while sticking to the same basic rules), but a series finale would be the perfect opportunity to provide some in-universe answers that don't lead to more scrutinising questions from people with "Genius at work" t-shirts.

The most popular fan theory for all the Springfield-weirdness is that it's due to the run off from the nuclear plant, although mutation via toxicity was already explored in the movie, so something a little more out there could be fun. Maybe it turns out Springfield is actually a post-apocalyptic reality made from the ashes of whatever unspecified destruction like out of the remaining fragments of pop culture that survived (an idea that has been explored from a reverse perspective by play Mr. Burns). Or perhaps it truly is all a dream ("let's burn rubber, baby!") Maybe God's not God, because he didn't make them in his own image, and the real universe creator is actually Ullman show-era Simpsons?

I don't know, I'm not a Simpsons writer (my suggestion would be to add a new, hip character though), but the basic idea would be to give something back to the obsessive fans, marking the finale out as an essential (if tongue-in-cheek) episode.