It would change the FOV and framing, which was carefully done by the director in the first place.
Isometric views aren't like a traditional FPP or TPP, changing the framing changes a lot more than just giving you a bigger picture. Some jumps wouldn't work, some angles wouldn't and would have to be totally changed, enemy item and 3d model placements would be totally off. They'd have to really rebuild the game from scratch around a wide screen format.
Great interview, but it still has me concerned that the topic is danced around yet again. It still sounds like they're re-rending everything but the backgrounds which they say they're meticulously touching up for HD.