@DTS Engineer Yes, this is still possible, even with this constraint. If you intend on creating your .swiftpm project via Xcode, you can add local Swift packages. See the below image where I successfully build an Xcode App Playground project with a local package:
However, this will not work if you use the Swift Playgrounds app, so users should be aware of this limitation:
Also keep in mind that the package must only contain Swift code. If there is any non-Swift code, the project will refuse to build.