T'Challa is still technically king though. Even the Prime Minister referred to him as "Your Highness". Same goes for Akili. Just to reiterate, I find the democracy stupid and disrespectful to the concept of Wakanda but it really only undermines the themes of Black Panther, not actual storytelling, assuming a writer wants to go that route.
Ridley wants a version of T'Challa that is aggressive, manipulative, and isolated. He's telling a story about the fragility of power and secrets from T'Challa's past. It helps his story to give T'Challa an all encompassing political system as a rival, positioning him as an outsider discontent with the new status quo despite his own failings.
Another writer may not want to tell that kind of story. Coates didn't, he ignored the democracy as soon as it was created with stories about demons and space empires. If Redjack gets the book we'd probably get something like his initial pitch to Marvel, focused on T'Challa as Marvel's Doc Savage on overseas adventures. Or we get a war epic from David Walker. I don't think there's a hard editorial mandate that the democracy be referenced or incorporated into every BP story. But there is a legitimate concern that it becomes the trend and we get more writers that simply choose to make the democracy the centerpiece of BP stories moving forward.