Can Naruto or Sasuke be promoted directly from Genin to Hokage? I'm just wondering if one of them (Naruto and Sasuke) becomes Hokage, is he promoted from Genin rank directly to Hokage?
While I am not 100% sure about the transition from Genin to Kage, I do know that Gaara was at most a Chuunin before becoming the Kazekage.  So, it would seem that a jump in ranks would be justified under special conditions of ability.

In any case, why should there be a need for a direct promotion?  If Naruto (or Sasuke I guess) has plans to become Hokage, it does not mean that they have an intention to skip the transitions between ranks (although I'm sure there would be some sort of allowance for them to "test out").