There is an important caveat to note when recommending this: path dependencies are invalid for versioned releases. (For hopefully obvious reasons; most paths point at different things depending on the context into which the release was fetched. There may be a case for enabling relative paths which do not escape the package, but to my knowledge that has not yet been considered separately from the general use case of a neighbouring package developed in tandem. So using an internal path will appear to work until you tag a release, but then a client will try to use your release and be told by SwiftPM that your package is invalid.)
I doubt it. I think this and another thread from a day or two ago were the first time I heard about anyone wanting to use it this way. All design, discussions, issues, troubleshooting, etc. that I can remember all dealt with relative paths pointing outside the package. Things inside the package being different was never on anyone’s mind. I may have missed or forgotten something, but as far as I know you have basically just pitched a brand new idea here.