9. Herb's Baby Translator Would've Totally Changed The World
While The Simpsons has a fairly loose approach to its own internal continuity, one of its most societally wide-reaching implications occurred in season three's classic episode "Brother, Can You Spare Two Dimes?"
The episode marks the second appearance of Homer's half-brother Herb (Danny DeVito), who invents a device which can translate baby babble into articulate spoken English, allowing parents to respond directly to their child's needs.
The product is unsurprisingly an instant hit and brings Herb great wealth once again, yet the device's existence has never been mentioned again nor has it even appeared in Easter egg form in any episode.
Presumably the writers realised that the world-changing inevitability of such a device was just too challenging to deal with.
Even so, for all intents and purposes this hardware absolutely exists in the show's universe and would've fundamentally altered child-rearing around the globe.