The ball is in Brock Lesnar's court.
During Extreme Rules, Kurt Angle addressed the situation with WWE and Brock Lesnar in a backstage interview. He said Lesnar was refusing to fight any contenders including the winner of the canceled number one contender match. Angle said Lesnar could come to Raw or come to terms for his next opponent and otherwise he would stripped of the WWE Universal Championship.
Angle's ultimatum can be heard in the following tweet.
Lesnar has not been on WWE programming since the Greatest Royal Rumble event when he retained the Universal Championship against Roman Reigns. In the meantime, he appeared at UFC 226 and positioned himself to challenge the UFC Heavyweight Champion Daniel Cormier.
Lesnar is not eligible to fight in UFC until January 2019 because of a six month suspension under USADA.