I believe that the way that users get, and developers distribute, software across different operating systems defines how the platforms cooperate with each other. Moreover I think that how it works today, i.e. on each platform we use both different store and different installation interface, in my opinion, exacerbates an isolation between them, makes it difficult for users with different OSes to cooperate and causes that they focus on choosing a suitable software, rather than on the job they have to do itself.
From my point of view, if we would normalize it - the way we get (and distribute) software, we would blur the line between operating systems and would create one, general environment for working (and playing), where operating systems are just interfaces defining how we feel the environment and not (like it is now with apps that work on some OSes and do not on others) whether we can even be part of it.
And even though the subject of these considerations is not making all apps crossplatform now, I think we could talk about a general space with software, one for all operating systems, which gathers and lists software for all of them, where one can search for apps available on all desired ones.
I see it as a place which one enable to discover and buy apps, but when it comes to installation - redirects to proper installation interfaces (you can learn more about a prototype of such a solution here
https://www.producthunt.com/post...). This way it enables to find software available on all operating systems we use, treats official app stores just as installation interfaces and creates the mentioned open, general environment.