The movie should have acted as a finale and it should have been an hour and a half long. It'd be full of outrageous shit. Marge will be cuckolding Homer with every single celebrity guest that's ever been on the show (even the dead ones), with the entire episode just being Marge getting fucked one by one while Homer just sits in the corner, crying as he jerks off and eats a sandwich.
The B-plot will be Lisa becoming transgender, then kicking Bart in the balls nonstop. No cutaways or anything, it's literally just Lester (FtM Lisa) kicking Bart in the balls while screaming about he needs to check his cis white male privilege. Every single person in Springfield will take her side, especially the celebrity guests who are fucking Marge.
It ends with the Simpsons insulting the viewers for being such fucking idiots for continuing to keep them on the air, then they all have an incestuous orgy right in the middle of the living room before vomiting all over each other and slicing their throats. Dr Nick pokes his head in and says "BYE EVERYBODY!", because "LOL REMEMBER WHEN THAT JOKE WAS RELEVANT? XD". Also, he's getting raped by Moe right outside the Simpsons house. Then Selma's Chinese kid walks on screen, waves her hands, and says "That's all, folks!"
The remaining 40 minutes are just the writers giving up: videos of them shitting on each other, having a huge orgy while covered in shit, footage of people getting shot in the head, people getting sucked and fucked, etc. You name it, they have it all. The final 10 minutes are just Matt Groening spun from intravenously injecting meth (the trackmarks on his arm would visible), screaming into the camera about how much he hates his life before pulling out a shotgun and blowing his fucking brains out all over the wall.
It'll end up being so viewed and talked about, that it renews the Simpsons for another 10 seasons.