It's a simpler solution is just to wait until legal situation is clearer.
QEMU is (mostly) GPL 2.0 licensed, meaning (most) code contributions need to be GPL 2.0 compatible [0]. Let's say, hypothetically, there's a code contribution added by some patch involving gen AI code which is derived/memorised/copied from non-GPL compatible code [1]. Then, hypothetically, a legal case sets precedent that gen AI FOSS code must re-apply the license of the original derived/memorised/copied code. QEMU maintainers would probably need to roll back all those incompatible code contributions. After some time, those code contributions could have ended up with downstream callers which also need to be rewritten (even in CI code).
It might be possible to first say "only CI code which is clearly labelled as 'DO NOT RE-USE: AI' or some such". But the maintainers would still need to go through and rewrite those parts of the CI code if this hypothetical plays out. Plus it adds extra work to reviews and merge processes etc.
it's just less work and less drama for everyone involved to say "no thank you (for now)".
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caveat: IANAL, and licensing is not my specific expertise (but i would quite like it to be one day)
[0]: https://github.com/qemu/qemu/blob/master/LICENSE
[1]: e.g. No license / MPL / Apache / Aritistic / Creative Commons https://www.gnu.org/licenses/license-list.html#NonFreeSoftwa...