I'm guessing United rolled this beta feature out to encourage buy-ups and it seems to be working. I've been #4 for 6 available seats ORD-BCN on Thursday night for days. In the last few hours, I'm still #4 but for 3 available seats -- guessing some people at #7 or below saw their positions and decided to buy up instead of play the upgrade lottery. I'm in Premium Plus already so not going to spend the money to snag one of those 3 seats; I can get a better dinner than the Polaris Lounge offers for far less.