i think that maybe the fourth will develop the rasengan based on the chidori as the problem with the chidori is the flaw with the counter, the rasengan might not have that flaw and maybe kakashi might have the same experience as his father, where he must choose between saving his team or the mission. he will choose the mission and his friends will die and from there he understands how friends are more important (thats the first thing he said to his own team (team 7) )