So it's official : https://www.nintendolife.com/news/2021/03/bethesdas_future_games_will_be_where_game_pass_exists
Future Bethesda games will be released "where Game Pass exists".
Phil Spencer's quote:
"So obviously, I can't sit here and say every Bethesda game is exclusive, because we know that's not true, there's contractual obligations that we're gonna see through as we always do in every one of these instances. We have games that exist on other platforms, and we're gonna go support those games on the platforms they're on. There's communities of players, we love those communities, and we'll continue to invest in them. And even in the future, there might be things that have their contractual things or legacy on different platforms that we'll go do."
"But, if you're an Xbox customer, the thing I want you to know is this is about delivering great exclusive games for you, that ship on platforms where Game Pass exists. And that's our goal, that's why we're doing this, that's the root of this partnership that we're building, and the creative capability we will be able to bring to market for Xbox customers is gonna be the best it's ever been for Xbox after we're done here."