Oh, that UI paradigm already exist. It's just that browser makers are too busy with things like webasm, webgpu, or allowing pages to launch location/notification popups at users, so they don't have time to fix fundamental flaws.

I don't think it does? Popups are one thing, but the very possibility of dynamic content entails that stuff will shift on the page. Sometimes it's just the nature of the thing, like a chatroom or a notification stream -- it'll shift as new content arrives, which is what I want most of the time, but if I'm interacting with a message, that message shouldn't shift. I'd like a general solution to this. Does that exist?