I'm just getting started in iOS development as a hobby, but what does this mean? Can I now build my app in Xcode with an Android target and use that binary in the Play Store? It surely can't be that easy now is it?
No. The vision document[1] lays out the direction of travel. Currently the focus is on shared business logic and libraries, rather than full native applications (although that's certainly a goal, albeit a very long term one).
[1]: https://github.com/swiftlang/swift-evolution/pull/2946/files
This doc you linked is from August.
The blog post from today includes, in fact at the very top an XCode Swift project emulating a Pixel 9.
The docs include a detailed Getting Started for Android and they even have an Android examples repo.
Hence the SDK.
By all means, it very much is possible to build Android Swift apps in XCode.
https://www.swift.org/documentation/articles/swift-sdk-for-a...
You can build the Swift part in Xcode, VSCode or your favorite editor. But the Android builds don't work with Xcode today.
Without Skip, you can still share other code through JNI - similar to Kotlin Multiplatform.
But it's not there yet
(disclaimer: I work on the Skip.tools product)
The example Activty I saw is pretty rough ergonomically, but I have no doubt an ergonomic, SwiftUI-like library could be built on top of what’s currently there and/or on the roadmap.
Same way there are C compilers for Windows and Linux, but that does not mean binary compatibility.