First of all, no, he doesn't have a second element. However, I do think he has the ability to use a second element.
Actually, most of the jounin and upper level shinobi can manipulate more than one element. They just can't use them as effectively as their affinity.
For some reason, if it ever happened, I think Naruto would be able to use Suiton.
But that could be just me being under the influence of his whole familys' names.
As for your going against Sasuke statement. Sasuke seems to rely on lightning based techs more than katon. Wind has the upper hand against lightning.
Meh, he has KM now, I doubt Sasuke's katon would pose much of a threat for him.