Products that can no longer be improved upon

In any meaningful way. So this doesnt include, for example, changing the colour to something you prefer.

Toilet paper? Hard to see how one would improve upon the current offering. You can get ample sheets, each one cushioned, some of them even fragranced. Perhaps a fundamental reworking of the whole arse wiping principle? Incidentally, what were those shells in demolition man for?

Arse jets have led to a repurposing of toilet paper. You still need it but only to dab away moisture.

The arse jets on 1980s bidets were outlawed some years back. Something about the lack of a non return valve polluting the water. Are these making a comeback?

Mobile phones. It's at the point where the new model offers so few and marginal benefits over the 'old' model.

Mobile phones (cellframes?) continue to improve massively every year. Cameras, processing speed, software, biometrics, apps etc all massively improving each year.

Some people don't have the imagination or ambition to explore the possibilities, but that doesn't mean the cellframes aren't better.