The implementation for this would most likely be primarily on the SwiftPM side. We'd at least need some support for the new artifact type in Swift Build PIF generation. Probably no changes needed on the Swift Build side as far as I can think of at the moment (not sure if that's what you meant by "for free").
It is working for the golden path use cases on the standard deployments of the most popular architectures of a handful of the most popular Linux-based operating systems, yes. That’s a far cry from full generalization to all possible Linux ABIs, which is not something I’m sure we should even attempt. There’s some great discussion on the Linux ABI problem in the original binary dependencies pitch thread: [PITCH] Support for binary dependencies
Also, the swift-syntax prebuilts are fundamentally a performance optimization of the build process, where we always have the option to fall back to building from source if needed. In my view that’s a distinct use case from binary artifact dependencies for the build outputs.