Naruto is defiantly the 6th Hokage in the future, in my book. He already improved so much, i say he needs to take just about 3 more steps on the latter, THATS ALL. I say once he learns how to control the Kyubi inside fully, he would be a unstoppable ninja. That of course he doesnt fully exert its force, since it does shorten his life faster, unfortunately. Why Masashi, Why?
Speaking of which the 4th and Naruto do have quite a resemblance, i cant doubt he might be his father, but it wasn't explained.