Couple of good suggestions here although IDK how realistic they are. Adobe and Valve obviously - if they could own steam or adobe, that would really make the MS store. Obviously any individual gaming house would help too. Would make the whole UWP effort much easier.
My idea in addition to Valve and Adobe would be FitBit. Probably wouldn't cost too much, and would be a path towards slowly phasing in/bringing in windows IoT to wearables. I wouldn't do that straight away, but perhaps the app system could be laid ontop of windows IoT core, or windows core, and it could be transitioned.
I also think something like Bitchute might not be a bad idea. Bings doing not too badly these days, and it might be a good idea to have a video sharing platform.
More realistic in terms of games, might be perhaps InExile, Bethsda, Sega, Square Enix and some of the others people have brought up.