A lot of Microsoft Office and adjacent programs have customizable UIs almost to the point of absurdity for decades yet it's uncommon to see anyone actually change the default layouts, adjust panes, or view modes.
Maybe it's because everyone hates toolbars and ribbons, but why? Perhaps it's that the number of options is overwhelming. I am fairly certain most humans have seen code and their naive impression is that it's "cluttered"/"noisy". That impression is not because it's text or a ton of buttons staring back, but the cognitive overhead of actually understanding what you're looking at. LLMs can create or suggest things, but the user still has to comprehend something to continue interacting. That's where the interaction falls apart.
What I can see is LLMs taking natural language input and curating catalogs of software or plugins. As it stands searching for software by feature is a terrible experience even for devs.
When the UX is not a barrier, people love customizing their devices! My collogues of all abilities use different Outlook themes, and everybody's mother and their dog have changed their backgrounds and ringtones.
Backgrounds and ringtones don't require any meaningful comprehension. It makes a lot of sense to assume the user would get an itch to stop looking at the same pictures and hearing the same ringtones all the time. That's as far as their desire for customization would go. It's similar to why cars have stereos and paint colors. Anyone can pay money for more customization, but few do.
Inbox rules are just about the simplest actually useful thing someone might do, but probably doesn't. That's a pretty clear signal to me they don't care. That end user cognition is the actual barrier.
In so many words, the user is dumb and complacent. Computers aren't going to think for them no matter how advanced the AI. They also don't want the computer thinking for them.
They want to get things done with stability. Computers are not their focus in life. Imagine an office full of people constantly changing how they work and forcing and politicking their bullshit onto other people (like devs do all the time). That's a normal person's nightmare.
Currently if I desire to make the "new mail" button always available, some technical individual would have to devote hours of their time to figuring out the required changes.
Replace a technical individual with an LLM and the story becomes completely different. People love complaining! If that's all that's required to make changes then I bet we'd see a lot more of it.
Pleasing everyone was never a people problem or a logic puzzle. It's fundamentally intractable and trivial to see how quickly contradictions would arise in any meaningful set of rules.