The only trouble with inviting people outside AA is the limited grid. We could potentially run a 2 grid thing, but that'll mean there is a pre-qualifying period.
Advertising will be easy enough as we can also use the LFS forum so people know, as well as server messages.
I was thinking that large fields could be handled with heats, like they do in athletics. It would involve a bit more organisation, and participants would need to keep a close eye on the rankings and grid announcements, but it could work...