I mean, this is pure ageism. Fujibayashi is an average middle aged guy, and Auonuma isn't even retirement age in France. I dunno if Aonuma wants to work into his 70s, but if he does, he's certainly mentally and artistically capable to keep going for another decade.
Would Fujibiyashi step into a producer role, should Aonuma go full Creative Fellow over the next five years? Probably. The three big planners on Tears of the Kingdom (Yohei Fujino, Mari Shirakawa, Yasutaka Takeuchi) all seem to have the kind of background to step into that role. We'll see who, if anyone, is Fujibayashi's number 2 over the next few years. I'm rooting for Mari Shirakawa, if for no other reason than she came up through 2D Zelda, like Fujibiyashi did, and she also is the most senior, having directed Kirby: Mass Attack.