Separate language downloads is already a possibility, I think they mostly don't bother as they can just make a single version and ship worldwide on discs. But there are games where you have to download from another region to get the subbed language for instance (can't remember which one though XD)
Separate packages was talked about on GDC, the dev can create a shared package with common assets for all versions, and specific packages for each platform. It's also possible to add new packages in the future and they can freely override the content in the shared package.
With uwp they are also improving the installing experience. Developer will have full control on what's needed to play the game, and will have in game apis to redirect which packet has to be downloaded first, and the same will apply for updates which no longer have to be entirely downloaded so you can play. And lately they will add delta updates from many media content so the updates themselves should get a lot smaller as well.
Supersampling mode would render in 4k and downsample to 1080p, so you would need the 4k textures anyway. Though I think even at native 1080p rendering, there would be room from improving using higher quality textures.