Even though iOS users are generally pretty quick to upgrade looking at the current iOS adoption stats it looks like we’re headed for a 15% tax on users if your app wants to user the latest evolved feature and a lag on when this can be rolled out until sufficient users have loaded the latest OS image. Worse, an application that previously worked will suddenly not work or be un-upgradable or previous versions of the app need to be supported if the user does not/can not upgrade their OS.
https://data.apteligent.com/ios/
I wrote about this in a digression off piste in Prepitch: Character integer literals
The tl;dr; it is the idea of shipping the Swift shared libraries with the operating system image seems to be flawed to me and they are better downloaded on demand by the app store app and installed to a central place in the file system where they can be versioned. This allows for all the advantages of shared distribution including saved resources on the device and allowing Apple to ship system frameworks written in Swift without tying Swift Evolution’s or developer’s hands or somehow hindering Apple’s commitment.
This said, unfortunately the ship has rather sailed on this now with Xcode 10.2 so mentioning this again may not be viewed as being particularly helpful but I have reservations about whether the course we have set is going to pan out - If it doesn’t this idea could always be introduced at a later date.