There's potential for a plug-in store to buy/rent them :)

Why not? It has worked on WP for years! Although, with the rise of AIs, perhaps not as much of a future in this...

But customized websites I'm sure people would like to have.

There is also the argument that Web may be moving toward an internet of bots (AI agents), where how the interface looks and feels to a human may not be as much of a priority as it will be how easy it is to be accessible to these AI agents. Not that this is a great development direction for humans, who would become less needed for a growing number of tasks.