Swift-Build is the Xcode build system, and it's open-source now.
So I think (I'm not sure if I've got this completely right) it could be in-scope to ask for those kinds of build-system improvements alongside language changes, and we could potentially even implement it ourselves and see how it feels. I believe you can also run Xcode with a self-built build system, so we wouldn't even need to wait for the next Xcode release to try it.