like how it happened with unreal tournament on ps3?
mods like new armours or locations are pretty much unofficial DLC
it's not impossible, and sony right now is endorsing the feature on user generated content.
the obstacles to overcome are the quality control and their distribution but i can see a few solutions to come up a few years later
one day...one day...
An FPS where you make maps is one thing, and I'm surprised they can control the cheating in that.
Making a mod in a game with such a scope as Skyrim I don't ever see happening. Even if they gave free textures to use for the console, someone would find a way to edit those textures, make a nvde mod, upload it and then some kid is going to play it infront of their parents and laws suites will start appearing.
There is just way too many things that can happen for me to ever see it happening.