Cruise might not be seriously committed to playing an ape one day (as Dylan Clark did indicate) – but on the other hand, it wouldn’t be that far a cry from most of his recent roles. The actor is famous for performing as many of his own stunts as possible – including those that are legitimately dangerous for the Mission: Impossible franchise – and has said on multiple occasions that he’s been attracted to physically-challenging roles of late. Motion-capture performances in general tend to fall on the more physically-demanding side (especially those from the Planet of the Apes series and similar tentpoles); which is to say that if Cruise ever does appear in a Planet of the Apes film, it might be in the form of a digitally-rendered ape, for related reasons.
As mentioned before, it doesn’t sound as though Cruise is genuinely intent on joining the Planet of the Apes series – and he already has plenty of other franchise movies to keep himself busy with, over the next few years (including, Mission: Impossible 6 and Edge of Tomorrow 2). Still, who knows; if the current Planet of the Apes franchise does continue after Caesear’s story is over, maybe it will be Tom Cruise (the CGI ape) who takes his place as the series protagonist.