And if you really wanted to, maybe made some concessions, and were clever about it, you could maybe find a way so that users define shapes and functionality and a default light/dark color scheme, but applications could still use the "user style" with their own color scheme, and allow the user to switch between that and the user defined colors.

It would also have the side effect of ejecting the people who just change things to make their mark. There is no more mark to make! Except making the "style configurator" for the user better, collaborating on expanding the protocol shared between it and websites/applications. You can invent a new type of button, put it on the pile, and hope it becomes one of the higher rated ones that gets downloaded and used a lot, on any OS, in any application or website. That will be a lot less interesting for hack frauds, and software interfaces can finally become awesome and then just better from there.