Being a Moderator for an architectural kata session isn't hard, but there are a couple of requirements that must be obeyed if the group is to have an optimal experience:
You must have sat through a run of the architectural katas. The reason for this rule is simple: it's far easier to see what the Moderator role is like when you've seen it in action. Plus, that way you get a feel for what the event is like, overall, and understand a bit more of the "vibe" behind it.
You must be able to think on your feet. Let me be 100% honest with you here: a large part of being the Moderator is answering the various "customer" questions that come up, and the kata proposals don't help you a whole lot here--they're deliberately written to be vague, offering up lots of room for flexibility and interpretation. That means you, dear Moderator, have to be willing to make up answers on the fly (and remember them later, during the Peer Review Phase!) when project teams ask you questions you'd never considered before.
You must be willing to facilitate. Part of the Moderator's job is to keep the group moving along at a speedy clip, so all the project teams can get their Peer Review Phase in before time expires. (This is something I keep hoping I'll get better at, just for the record.) You also have to be willing to step in and redirect conversation when it threatens to get out of hand, either because the group is falling into the "you suck/I rock" Dichotomy, or because the group is debating a particular point just a little too long. This requires a degree of diplomacy and finesse and tact. Or else a really loud voice.
Your group must come up with a new Kata for the site. The katas will only be as interesting as the ones that are generated by the community, so as a "licensing requirement", I ask that any group that runs the katas to wander on over to the Architectural Katas Google Group and suggest a new Kata idea for possible inclusion.
Beyond this, you should have some development experience, and ideally you've spent at least a little time as a software architect, but I don't think that's absolutely necessary, to be honest.