Quite honestly, I can't imagine Bethesda Game Works spending their time on something at that level. Their resources are much more valuable than that. Their own IP would net them far more money than Nintendo would ever pay for an exclusive. Elder Scrolls is way beyond Metroid in that regard. It would be like trying to hire The Rock to work for a local indie wrestling show at the bingo hall.
And, personally, I want them working on another Elder Scrolls instead of doing something else, especially a project that would never come to PC. I'd rather have the next Elder Scrolls than any Nintendo IP (or Sony, or Microsoft).
id Software is the only fully-functional "Bethesda" developer that doesn't seem to have their hands full. The only other studio would be the new Bethesda team in Canada but I just can't imagine an outside IP being their first project.