Allowing plugins to generate mixed-language sources

With the SE-0541 PR merged, is there anything that would speak against allowing plugins to generate C files into Swift targets when experimentalCGen is enabled? I put an agent to the task and for my rather simple use case (C file that calls functions declared in Swift, but is not referenced from Swift source), it was enough to remove the checks in SwiftModuleBuildDescription.swift and TargetSourcesBuilder.swift to make it work. For context, I have a PoC for Swift-PHP interop that I would like t...