Thank you all for your feedback! I really appreciate the help.
My main concern is definitely location. Since AB is a big convention with a lot of panels, etc., it would be difficult to have a location for gym leaders to set up camp. I thought it might be a hall event, but then there's the risk of impeding traffic. If I can get the rest of my ducks in a row, though, hopefully it will work out.
Maybe I can try to wrangle up interest through the AB forum or tumblr; even if we start out small (which is likely, given that we've only got a few months to prepare), we can get our feet wet this year. Actually, where it's a new event, it might be beneficial to have a small league the first time around, to gauge what does and doesn't work and see if this is something to pursue annually.
At any rate, I've got plenty of things to think about, so thanks a bunch for that! I'll have to start planning to see if we can't get this thing off the ground.