Foundation is going through a gradual open-source rewrite by Apple and the Swift community, which is going to take a while but will eventually open up Swift more to other platforms.
By the time the Swift project eventually has a great message to share on that, there could well be hardly any non-iOS/macOS developers listening. Look at the last 5-10 years. The momentum gap between e.g. Rust and Swift in the wider development community is gargantuan.
IMO if Swift had had a great multiplatform toolchain/developer-experience in the ~2015-2019 timeframe then it could have established itself as the no-brainer C++ successor. But that moment has passed and they squandered the opportunity.
Yeah I have high hopes for the new Foundation. The current open source Foundation is OK but it doesn't quite match what's there on Apple platforms and makes it all a bit difficult. Having one shared implementation should improve things.
It's still funny how this is positively encouraged by HN and yet .NET receives constant stream of FUD and criticism for already being what Swift wishes to be in some 5 to 10 years in terms of being platform agnostic (both the runtime and the tools).
