I was also wondering about the whole “AI content is not copyrightable” thing… Does that potentially screw up copyleft licences?

In practice, no. Simply containing AI content doesn't invalidate copyright or licenses.

Purely AI generated content is not copyrightable, but the Linux kernel does not fall under that category.

Works that have a human in the loop are, for the parts that are human created, copyrightable. So if a developer uses AI to assist them in writing code (fixing formatting, detecting bugs, refactoring) then the code is copyrightable.

Someone could technically take the AI generated portions of the Linux kernel and use them outside of the licensing restrictions... but since it isn't possible to determine which lines of code were AI generated and which were human generated then it is very risky to do. If they were sued by the Linux Foundation, and found to have used code that was verifiably human-written (a developer testifying that they personally wrote the code in question would satisfy that requirement) then they would be civilly liable.

Since the Linux kernel is mostly human-written, simply extracting the AI-written parts would likely not provide any actual useful functionality and it would come with the risk of violating copyright if you chose the wrong lines to copy. It's a large risk for very little reward.

After all, why copy AI generated code which would potentially lead to you being sued when you can just make your own AI generated code.