So playing I'm playing on the 360 and was wondering whats with the gate near southfringe sanctum? Is it for some unreleased dlc that never came out?

It's probably there for immersion purposes. That road in particular leads to Cyrodill I believe. There is also another gate that leads to Hammerfell and Morrowind.

I think you mean the gate to the south of Skyrim. It's the way to Cyrodiil, it's been there since 11.11.11. I think it hasn't anything to do with DLCs rather for decoration.