Marge opens a door that has never been opened before, finds behind it a small closet with a switch marked "Time" and a sign below it says "Don't switch this switch unless you REALLY REALLY mean it!"
Of course, Marge does, and instantly becomes 49 years old. This was the switch that prevented time from passing in the Simpsons!
Lots of potential, with maybe the switch being continually switched, alternate destinies, alternate pasts.
"I dunno - you kids are WAY overdue for a growth spurt!"