Star Trek (2009) brought back Leonard Nimoy in his iconic role, using him as Spock Prime in the Kelvin Timeline. His character came face to face with Zachary Quinto's Spock in a way that worked surprisingly well, both for the movie and for Nimoy, who said he "found a certain peace with the character." And Star Trek: Strange New Worlds could now have that same opportunity, just with different characters.
Recently, William Shatner has expressed a willingness to return as a de-aged Captain James T. Kirk if the story idea was good enough. He made it clear he won't do cameos so it would have to be a strong storyline with more than just a few minutes of screen time for the acting legend. One way to bring Shatner back would be to have his Captain Kirk face off with Paul Wesley who plays the current Lt. Kirk on Strange New Worlds. If done properly, this could be an incredible piece of work.
Other than the fact that he has aged, Shatner is still Kirk. And perhaps bringing him in to either confront Wesley's Kirk over an important decision or to walk the entire Enterprise crew through a tricky situation if Captain Pike (Anson Mount) wasn't available would be a definite boon for the series. The use of time travel would make this a breeze.
Strange New Worlds doesn't need any help with ratings as it's one of Trek's best series; however, Kirk facing Kirk much like Spock faced Spock would be a pivotal moment in Star Trek history, especially since it would, most likely, be the last time we would see Shatner as Kirk.
This could also work without the use of de-aging if Shatner were amenable, with Lt. Kirk seeing himself in the future much like Pike saw his own future. This could also serve as a retcon for Kirk's death in Star Trek: Generations, which wouldn't upset any fan in the Trek community. Otherwise, having a sixty-something Kirk meeting a younger version of himself aboard the Enterprise would be a perfect way to say a final goodbye to the beloved captain.