Irving and Hayward will be 28 and 30 then and getting paid the max/superman again. Everyone can't be paid.Kyrie's been the MVP of the team. The only other player who could be considered is Horford. Brown's been nice but he ain't MVP of this squad.
Brown is under a rookie contract and the Cs have him until 2020 (assuming they exercise the team option to keep him in 2019/20). Then they can make a qualifying offer for him in 2020/21. And by that time, he (and Tatum) will be taking the reigns from Irving/Hayward/Horford. And that's how Stevens and Ainge want it to be.