I love the concept, but I too am concerned about the time frame. I think you'd probably want to limit the swap to really long term swap veteran types, because I would for see the chance of losing loads of people who just quit the board, as extremely high.
Having said that, if you can work out the kinks, I would totally join this swap. Since I've had kids, my birthday has always been a bit low key, and I never get ponies.