If there's going to be more DLC, it'll be after the release of Ninja Gaiden 3 Razor for the WiiU. I saw that short teaser of it during the Nintendo conference at E3, and Ryu was using his blade Ninpo from Ninja Gaiden 2. So it's possible new Ninpo or weapons could be DLC.
It strains the mind a bit don'it? You think you're all alone... maybe I come down the chimney, bring presents to the good girls and boys. Maybe not, though. Maybe I've always been here.