The Outer Worlds had already entered a publishing deal with Private Division before Microsoft acquired Obsidian, and Minecraft was already a released product.. I wouldn't hold your breath given that Obsidian's upcoming titles Grounded and Avowed are both Xbox/Windows 10 exclusive.

It's possible they'll think on Fallout, TES or other franchises that already have a long history on Playstation being available there.. but I doubt it.

Doesn't seem like it.. Halo, Gears of War 5, Flight Simulator 2020.. those are all on Steam as well as the Microsoft store. It does require you to login after launching those titles on Steam but it's all contained with-in the game, and apparently with a small enough amount of crazy middleware that you can even play Halo The Master Chief Collection under Linux using Proton. I think Microsoft is very much aware that trying to keep major games like these exclusive to the Microsoft store isn't a great idea, a lot of people never open, let alone use it.