Does it matter if it comes from a human you don't know or an AI you don't know? If it's difficult to review for the maintainers, then the maintainers should not merge it.
Let me put it this way: if a random contributor opens a PR as a human, then the maintainers will do what they were doing before AI, right? Now if a random contributor opens a PR pretending to be written manually, but actually written with the help of an AI, what will the maintainers do? Exactly the same, right? Try to read and understand the contribution, and merge it if they want to take responsibility of it.
The difference, really, is that everyone and their dog can now open a PR that looks evolved, and for maintainers it's difficult because it adds noise.
Sure. But I'd trust someone whom I know to be a domain expert and a good coder much more than some random github account. And once I see anything like "co-authored-by: claude"... oh hell no I'll go over that with a fine toothed comb because I have zero idea what the user prompted into the LLM, which in turn means I don't know what edge cases the author (and by extension the LLM) even knew about.
As a maintainer, if it's easier for me to ask an AI to do it, then I will do that. Now depends on what "easier" is. Maybe a question of trust (if I don't trust a random contributor, I may as well do it myself), maybe a question of testing it (if a contributor can show me that it works on their 5 devices I don't own, it may have value).
But the fact that it was written by AI is not the biggest factor, IMO. Proven by the fact that if the AI writes exactly what I wanted, then I will be happy to merge it.
For one, LLMs tend to waffle and produce code that works but is much more extensive and/or unintuitively organized than code that a human writes. The bigger thing however is testing. LLM code tends to test itself, whereas a domain expert human tends to have many more domain-specific edge cases in mind.