This is basically a new season of different battle type to Random Match-up named Rated Battle.
The feature was available in BW (2). All you had to do was set up a Pokemon GL account and then log-in on your DS when you enter the WiFi battling selection at the Pokemon center.
At first your given a default rating and you battle people of the same rating, but if you win you gain a higher rating and then next time you challenge people of your new rating.
It's like a WiFi laddering system.