First person does not define this series. First person does not define "immersion".
That's just playing on words. Immersion is created by a number of factors : the art, the point of view, the sounds and music, the lore, and the way you are involved in the adventure.
The art is less realistic, thus less immersive. The main PoV will be third person, wich is less immersive than first person (just look at all those mods for Oblivion, Skyrim and Fallout wich change your journal to first person writing). The sounds and music, can't say anything, let's wait and see. For the involvement, even if the battle break with the traditional WoW-like combat, it will still be non-real-time combat, wich is less immersive than real-time combat. Yet, seems like they got the exploration part right, so let's wait and see for that one too, same for the lore.
Overall, the art and the gameplay elements will make TES:O less immersive than the solo games. Wich doesn't mean that immersing yourself in it's universe will be impossible, but it will be harder.
Elder Scrolls is defined by its lore, background and feel. I think it does not matter if you play it on 1st, 3rd or even on a table with your character on a paper, it will still TES.
I'd kill for a TES pen & paper RPG. I wonder why Bethesda didn't made one already, they have more than enough material to do this.