Ideally, there should be a way to cross-buy games on consoles and PC. For movies and TV, there's that DRM locker Movies Anywhere (and there was also UltraViolet - R.I.P.) which can be linked to purchases made on Google, Microsoft, DirecTV, VUDU, Apple, and various other media storefronts. Therefore, no matter what movies or TV shows you buy, they will appear on other services as well. I would assume this also includes media not available on every service, although I wouldn't take that as gospel truth.
Linking accounts together is fine, but IMHO it seems a little messy without some sort of central account linking hub. Also, I don't know if console exclusives would be featured on other consoles, i.e. Mario Kart 8 Deluxe on PlayStation 5. While that sounds awesome, it's highly unlikely; my assumption would be it would be reserved more for triple A third party publishers and indies that have the same games on multiple platforms - Ubisoft, Bethesda, Activision Blizzard, Cyan, Atooi, No More Robots, Image & Form... just to name a few I know of.