This is incredible news for anyone who is a fan of single player games. I can't think of a western publisher that has done a better job of providing tons of high quality single player experiences across different genres than Bethesda Softworks. Prey, Dishonored, Wolfenstein, Doom, Fallout, Elder Scrolls, Rage, Evil Within, etc all recently. And upcoming with Ghostwire and Deathloop. What a huge deal for Xbox.
Personally I see them releasing the mega big games on PS5 but most of the stuff being MS exclusive and all of it coming to GamePass day one. I doubt MS minds letting PS5 owners buy copies of Fallout 5 for $70 a pop while they sell GamePass subscriptions by putting the game on the service at no charge.
Also this makes New Vegas 2 a real possibility. Microsoft has the trifecta of western RPG power now with inXile, Bethesda, and Obsidian.