Shikamaru, although my favourite character is a slacker, who although has grown up considerably in Shippuden, still just is not the sort of person designed to have the role of Hokage. He IS a genius, and caring and all but is best suited to a role such as his dad's, Shikamaru also seems fine with the rank of chunnin and doesn't seem to want to rank up or rank down.
Shikamarus incredibly intelligent, but the role of Hokage requires more than that.
Just let's put it this way pain attacks konoha you got a shikamaru as hokage b naruto as hokage
I do agree with the fact Naruto would make a more fitting hokage than shikamaru, but think about another situation. At the hokage summit, remember how Gaara verbally embarrassed the other Kages? Shikamaru, despite his age would be able to lead his village and plan good strategies- basically how it happens in the real world.
Imagine Naruto in that situation as immature as he is now. It just wouldn't work out, Naruto must be hokage- but he still has a hell of a lot of growing up to do beforehand.