You make a really good point, I'm not sure if the other kage's would ever appoint a permanent leader for all ninja but if try did it would be naruto and he could 'bring a great change to the ninja world' other than that the only way he could influence the entire world would be to move about through it meaning not being the Hokage. But I really want him to become Hokage... Obviously it's all he talked about in the original Naruto and now he saved the entire village and is finally there but he tells himself he could never be Hokage because he couldn't save sasuke. I feel so bad that he has put his dream on hold.
And Sasuke should never be even considered for Hokage, he has been manipulated too much for the village to trust him that exclusively. I mean he's so far gone he intended to kill his teammate to get to his enemy even though she had saved his life previously. Not really great stuff to put on his resume... Lol just my opinion! =)