My understanding is that Odyssey involved a complete rewrite of the engine. That means it should be much cleaner, more coherent code than it was before because all the additions have been melded instead of simply tacked on. It also could be taken to mean that Odyssey is, indeed, ED2. At least, I would argue that a new engine makes it a new game. Rewriting the engine also means that whatever mysteries were left behind by the original programmers are no longer there. So it should be easier for the team to tweak things going forward.
Honestly, I think making a "new" game would just be a marketing ploy. There's no functional benefit to abandoning this to start from scratch after just rebuilding this. Anything they might want to add to the "new" game could just as easily be added here. Which may have been part of the impetus behind the rewrite, enabling planned future features that would not have worked with the old engine.