What would end up in it, though? The kernel has a lot of conventions that are enforced by reviewers rather than written down anywhere. An AGENTS.md that only restates the documented ones saves nobody anything. I doubt the maintainers want to write down the stuff they currently catch by instinct, like which subsystem takes which kind of patch. If they don't, the file becomes a style guide nobody reads, same as the coding style doc is for most first-time contributors.