What about scaling the number of points awarded and lost in a game based on the standard dev of the ratings for the players involved? There's definitely been debate about whether say, a 1500/1500 team is a favorite or a dog against a 2000/1000 team, and this change would reflect some uncertainty about the fairness of such a matchup despite the average rating being the same. So, in the end, it's still zero-sum, but more incentivizes playing with people around your rating.