I would love to have a slice of stdlib in my app bundle that contains everything that the OS on which the app is running does not have in its glued stdlib. That would mean that Swift developers which stuck to some older OS’s will be limited by only some runtime related features, but would still be able to fully utilize the evolving stdlib.
I personally would also want to see a sliced runtime extension bundled with my app, so I can always use the latest and greatest language and stdlib features in my app like pre ABI stability. ABI stability might be great for Apple as they will avoid waste of space for apps in their data centers and on user devices, but for many of us developers it‘s feels like just like a kick in the butt (to be clear this is just critics so please take no offense by this).
I know there are technical boundaries for the things I wish, but it does not hurt anyone if I speak my issue with the ABI stability out loud. 