Just wanted to post a short positive note as someone who explicitly have avoided Foundation (for all the known reasons) - this looks like an excellent pragmatic approach and structuring modules based on possible external dependencies makes good sense.
For our use cases Essentials and Internationalization will cover all we want/need and having a native Swift implementation that is feature-for-feature (or bug-for-bug ;-)) compatible cross platform is very good news - much looking forward to see this unfold and to try it out soon and try to contribute as we can - and to reevaluate our (non-) usage of FoundationXXX.