>> they should just propagate deltas and display current state. It's a different way of thinking about how UI can work, but imho it has a lot of benefits aside from just speed and safety.

That's how delphi does it. Connect widget to a data source and it will update reactively when data source changes. And data source is accessible without touching the widget. When doing a batch update on data, you can also disable widget updates in order to make rendering faster. It also works both ways, so when data is changed from within the widget, the bound data source will be updated accordingly.