My point is that there is no way to deploy back any functionality that does not exist in the OS due to things like ABI stability. That means if apple frameworks use some swift internals, these things will stick with us forever because they cannot be swapped out on older OS‘s, which also could force us towards a design that is not ideal anymore (see how $ prefix was forced and how function builder design was kept for SwiftUI). Don‘t get me wrong, all I want to say is that I hope that these internals will be implemented as hooks that apple can use as they wish but that it does not effect any future direction or design of generalized features.
We've been careful to make the use of these experimental features not tie our hands with respect to ABI, typically through the use of @_alwaysEmitIntoClient. We may have to carry some older entry points forward in SwiftUI, but that doesn't affect Swift's evolution.