I don't know the future, you could be right, I just don't see the need for appstores on desktops.
Most software is like photoshop - used by professionals and have total control of the market.
Other, like firefox and vlc also dominate.
People don't look for applications anymore. The basic set fills almost all tasks. The exception to the above is games, those are being installed all the time, new ones appear, and not a single one dominates. An appstore just for games would make sense.
As of now there is no one app store that must be used with any of the desktop OSs. People won't give up freedom that they already have - to install whatever, whenever.
Phone makers want to control whatever they can, but users already unlock and break because those appstores, as fun and convenient as they might be, are the opposite to freedom. Some people don't care about freedom, untill they need some app, and they'll break the phone to get it.
So even now, those appstores with all their reported success and billions of downloads, don't tell the true story of how many phones are jailbroken and rooted to avoid the appstores, and what is the percentage of users that don't want an ecosystem.