Work is underway on Black Panther 3, and it's been widely reported that the movie will kick off the post-Avengers: Secret Wars MCU in February 2028. 
A mixture of rumours and even some leaked concept art from the next Avengers movies (we still don't know whether it was for Doomsday or Secret Wars) has led us to believe that the plan is to reintroduce T'Challa after Shuri took his place in 2021's Black Panther: Wakanda Forever.
Whether that's an adult version of Toussaint, a.k.a. Prince T'Challa II, or simply a new version of T'Challa who returns with a different face in the post-Secret Wars timeline, remains to be seen. However, based on Black Panther: Wakanda Forever's touching ending, Toussaint would arguably be the best way to continue honouring Chadwick Boseman. 
F1: The Movie star Damson Idris remains the apparent frontrunner to play the next Black Panther, and recently reignited speculation by appearing alongside Angela Bassett (Queen Ramonda) and Danai Gurira (Okoye) when they suited up for a catwalk appearance at Vogue World: Hollywood. 
Asked about the persistent Black Panther rumours at the TIME100 Next Gala, Idris grinned and replied, "No, no. I don't know anything about it [Laughs]."
Are we buying it? The actor may be having fun with the speculation (it's a good way to keep his name in the headlines, after all). However, he would be a great fit for the role, and his casting may end up being Avengers: Doomsday's biggest surprise. 
One actor we know will appear in Black Panther 3 is Oscar-winner Denzel Washington. While nothing has been confirmed, Achebe and Magneto are among the names we've since heard from scoopers claiming to know who the screen icon will play in the MCU threequel.
Doing the rounds to promote Sinners a few months ago, Coogler was asked about Washington's comments and said, "I’m dying to work with Denzel and I’m hoping we can make that happen. I got every intention of working with him in that movie and as long as he’s interested - it’s going to happen," he confirmed.
The filmmaker made a point of praising the Gladiator II star by calling him a "living legend and a great mentor," adding, "He's all about looking out for us." 
For now, Wright will reprise her role as Shuri in Avengers: Doomsday, where we believe she'll serve as a member of Captain America's Avengers.
You can watch Idris' reaction to being asked about playing Black Panther in the player below.