The last two TES games have been following a trend in that the people narrating the trailers end up voicing important characters in game - Patrick Stewart as Uriel Septim in Oblivion and Max von Sydow as Esbern in Skyrim. It seems all but confirmed that Gambon was narrating the trailer, and so it's likely that he will be voicing an important NPC in the game.

What NPC do you think he will be voicing? I'm personally hoping that he'll voice Vanus Galerion as that would be pretty badass.

That guys voice is pretty awesome. Not sure who he would be though, maybe Mannimarco. It will probably someone that all the factions will encounter and be a main player in the game.

http://www.elderscrollsonline.com/en/media/videos/147