I expect that one important difference here is that iPhones will still presumably run the Apple App Store out of the box / in parallel to whatever other answers

I expect that one important difference here is that iPhones will still presumably run the Apple App Store out of the box / in parallel to whatever other answers emerge. This differs from the Samsung / Amazon model because the initial store is likely to be less of a disaster, and different distribution mechanisms will perhaps become known for their quality, among other factors. You could imagine multiple app stores, in which you have a wild-west store but also the default Apple one and a "maker store" one focused on CAD apps and 3D printing gear and whatnot, with different levels of moderation / curation in each. (An aside -- whenever I look at the Apple App Store's home page, it always seems filled with all sorts of crap I'm uninterested in. I haven't used the Amazon or Samsung stores, but I hardly think the Apple App Store curation process has resulted in a paragon of quality...)