Oh wow, this is legitimately great policy: https://www.reddit.com/r/StreetFighter/comments/1uf2xkl/comment/otokvvb/?context=3 (via Audrey Watters' Second Breakfast)
The products of AI are unintentional approximations, therefore, AI generated content is off-topic.
That principle applies to so many contexts.
It's great, in part, because it's built on an acknowledgement of the value that motivates the community it governs. Fan communities are driven by recognition, appreciation, and enthusiasm for a topic. At best, an AI can only accomplish one of those three, and even that's more a matter of statistical probability than cognitive recognition. Excluding AI works may result in less polished submissions, but they'll be submissions more directly informed by those values.