As I have said in previous threads, I think this theory of yours has potential.
I agree that it's quite likely that Kellhus will replace Seswatha in future Dreams, since as MSJ said, what Seswatha tried to prevent already happened, his role could be considered complete (also, Akka is now the Seswatha figure of the story).
I think it would be interesting if Akka's first Kellhus Dream took place chronologically shortly after Akka renounced him, his School and Esmenet back in the spring of 4112. Akka could even "catch up" with significant events in Kellhus' life from the past 20 years over the course of the series.
Now, will anyone else have the Kellhus Dreams? Serwa would be an obvious choice here...it would be interesting to have her react to possibly learning quite a few things she didn't know about the father she idolized - especially after his Thousandfold Thought failed at the end of TUC. As for anyone else, I'd love it if one or more of the witches had survived and become secondary characters who also have the New Dreams. Having at least one other Mandati, such as Saccarees (if he survived, I think it's likely he could have) react to the Dreams would also be nice (Nautzera could even return in this capacity...).