You're assuming that everybody will be equally skilled in using an LLM to create software. I don't think anything in my experience indicates that this is true.
Sounds like the user could just ammend the software to his need with the LLM, but instead of sending that update to the maintainer with a pull request, just keep it to himself, to the users version.
A user would have to be someone who doesn’t have access to an LLM to make bespoke software themselves, and isn’t able to use existing software. I think that’s a vanishingly small segment of people.