Here’s one way I can think of doing it. Somebody announces the week’s theme via a blog post on Sunday; we can set up a rotation for this. We also announce at that time any changes to the games’ material limitations–I assume we’ll be restricting ourselves to commonly available gamer paraphernalia (6d12 is okay, a roulette wheel probably isn’t) and any paper you can print out. Regular participants should post in the comments whether they’ll be designing that week, and new people are welcome to stand up and be counted too.
I’d like to be able to hold at least one midweek meeting online, but with players from literally around the world, that will likely be difficult to coordinate. Maybe we can set up a wiki talk page and require that everybody post a status report on Wednesday. People should also start sketching their games in the wiki at this point, if they haven’t already.
Games are due by midnight in your local time zone on Saturday night; they should be posted in the wiki under that week’s heading. We can take Sunday to write up some commentary on each game’s talk page, and whoever’s next in the rotation can announce the next week’s theme.
Things for consideration: should we bother with a voting system for Game of the Week or whatever? I have a feeling that would be more discouraging to nonwinners than it would be encouraging to winners; it’d be more helpful to require everybody to post some kind of commentary on every game, whether it’s just “this is good” or “you need to change mechanic x because of y…”
Also considering making it a requirement that for your game to be officially listed under that week’s entries, you must have playtested a previous entry during the week. I’m not sure how many of us have regular gaming groups and could accomplish that, though; either way, we should try to get in a significant amount of post-submission playtesting (for others’ games and our own).