Coogler and Feige should continue the vision they originally had. It's plain as day T'Challa was going to be a key figure for the Avengers going forward and I think you quite literally have a once in a generation opportunity to define the Black Panther mythology through its originator. The consequences of opening Wakanda, the struggle of man vs king, his relationship with Nakia and the other tribes, these were plot points unique to T'Challa that deserve to be completed before Shuri or M'Baku take the throne for a sequel trilogy.
Of course Marvel could contrive a way for Shuri to become this super badass warrior and tech genius who is thrust into her brother's shoes. But outside the fact that for many it wouldn't feel organic or true to what she was supposed to be, I think T'Challa should be the one to complete Wakanda's integration on the world stage because it was choice. The only stumbling block is the tragic passing of Chadwick Boseman, but ultimately I think what T'Challa represents as an ideal for heroism should transcend his actor.
I can't speak for Boseman nor would I ever assume to know what he would want, but I think the way he framed every aspect of this movie in terms of its broader impact on black consciousness, there should be consideration given to allowing T'Challa to continue on being the hero he was. There will always be time for Shuri or Okoye or whoever to take the throne and define it for themselves, but I think T'Challa's arc is worthy of completion on account of how he brought us this world and should get the space to explore it for years to come.