Do you honestly believe that Bethesda has constructed an entire game engine from scratch
and developed an entire game in the standard 4 yr cycle?
Todd Howard: The technology is ours and it is inspired by the technology we have. We have a lot of it. But that's our starting point - the Fallout 3 tech. It started with Morrowind, we went to Oblivion, we did a lot between Oblivion and Fallout 3 because now we had final hardware - with Oblivion we had six months on final hardware, so Fallout 3 technically does a lot more than Oblivion. The new stuff is an even bigger jump from that.
The technology they
have, which is a highly altered and customized version of the Gamebryo engine. They can call it their own because it's middle-ware and the ability to alter the stock engine's core code is what makes it their own.
The engine is entirely new as in it's a new Gamebryo build, unlike FO3 and New Vegas which used the Oblivion build as a base starting point.
Given the fact that it was released at the exact same time as development on Skyrim began and seeing what Todd has said in the quote above I think it is a safe assumption they are continuing on the path they were on and using Gamebryo's latest engine. Mark my words ladies and gents, Skyrim
will be running on a Bethesda build of http://www.emergent.net/en/Gamebryo-LightSpeed/Features/. Bank on it.