What is something AI won't be able to do, if anything?

Creativity and originality --- think outside the box.

As in formulate a workable plan to achieve some goal that is decribed in general, non-technical terms.

I assume we're talking about LLMs here. Any results are some re-formulation of their training data. They can't/don't really venture beyond their training data or what can be found on the internet.

The internet is a great reference but it doesn't hold a ready made solution to every problem --- and neither does an LLM.

Worry about being replaced by humans all the time?

I don't get all this prevalent "AI will replace everyone!!" hysteria. AI might be indeed pretty good at writing small, self-contained pieces of code such as a simple app or an API usage sample (in reality, not creating, but rather quoting or combining others' code), but AI fails miserably and utterly at maintaining larger codebases, not to even mention large, commercial-grade code repos. All AI can produce en masse is pathetic spaghetti code with no real-world commercial value. It actually takes longer for a human programmer to un... screw what AI has written than to write it all from scratch in the first place.

dude... if your toilet clogs... you gonna call AI?