Huh, I’d usually say this kinda thing isn’t worth looking to deep into, but that seems kinda different than a typical PR answer.
Although the main thing is that before the Switch in 2017, Nintendo just didn’t have any Bethesda games, so I can’t really see any as a playable character since that would’ve had to have been planned since 2015.
However, I could see a Bethesda character in another role like a boss or assist trophy.
A boss could be a dragon from Skyrim, some big demon from Doom, or some mutant from Fallout (I’m the most knowledgeable person on Bethesda games).
A Vault Boy assist would be kinda funny. Not sure exactly what he could do, but it could work. He could be like Tingle where he has multiple random things he could do, with the activities taken from the different perk icons in Fallout.