A few other minor points as well. Basil the chambermaid ruled for 10 years or thereabouts before the emperor was becoming uppity during which times half the empire was in revolt making his authority weak and open to challenge from the emperor. Also when Basil II did make his move he was not the boy barely in his majority but a man of almost thirty and a lot more seasoned. Basil challenging anyone at a young age is much less likely.
I disagree.
"For years, at least since the death of Romanos II in 968, members of the military aristocracy, who ruled in the name of the legitimate Macedonian emperors, ahd controleled the empire. Now, in 976, the
domestikos Bardos skleros expected to continue that tradition,
and he rose in revolt when Basil II declared himself fit to rule on his own." (my bolding)
http://books.google.com/books?id=KIFJiOCSYc8C&pg=PA271&lpg=PA271&dq=Basil+II+ruled+in+his+own+name&source=bl&ots=n67_euv-nG&sig=Z9lUNyWSgTeK5-rxL6BIxE_iTis&hl=en&sa=X&ei=COejUpGtOcvioASv9YHIBw&ved=0CEIQ6AEwBA#v=onepage&q=Basil%20II%20ruled%20in%20his%20own%20name&f=false
So Basil is stating from eighteen on that he is not okay with someone taking John's place. Why would he be okay with John continuing to dominate affairs?
At best, this is going to take up time and energy for both men. At worst, one of them is going to die.
Related to the chamberlain: That he lasted nine years after possibly poisoning John does not suggest Basil expected to be poisoned by him, but it does suggest that Basil had had enough of him. And that's someone who can't take the purple, whether Basil dies or no. John
can keep it to himself by killing or blinding Basil.
So if John manages to stay alive somehow its likely he´ll get at least 10 years before problem starts to get beyond what can be managed. Also he is as much emperor as Basil is at that point and a popular to boot. Basil isnt a dumbass like his brother and wont go charging in on a fools quest. Incidently this PoD is likely to end up with Basil getting married since John would likely steer him in that direction to strengthen one alliance or another since he himself isnt likely to get any issue.
Not going in on a fool's quest doesn't mean very much when looking at how John got rid of Nicephorus II or Basil I got rid of certain people in his way.
And "can be managed" does not turn it into a nonissue that can be brushed aside as if they don't both intend to control the state's course.
I don't want to argue it would be impossible for them to get along, but two strong willed men each desiring supreme power is not a recipe for harmony.