An ever-shifting UI sounds unlearnable, and therefore unusable.
One problem LLM’s don’t fix is the misalignment between app developers’ incentives and users’ incentives. Since the developer controls the LLM, I imagine that a “smart” shifting UI would quickly devolve into automated dark patterns.
I'm with you on disliking dark patterns but it seems to me a separate issue.
Take for example world-building video games like Cities Skylines / Sim City or procedural sandboxes like Minecraft. There are 20-30 consistent buttons (tools) in the game's UX, while the rest of the game is an unbounded ever-shifting UI.