Swift 5 is ABI-stable on Darwin, it isn't on non-Darwin platforms. You will still need to redeploy stdlib/runtime even with a patch version change of the toolchain and the SDK (i.e. 5.9.0 to 5.9.1). For that reason alone I recommend statically linking on non-Darwin platforms. As for binary size concerns, IMO those should be discussed in the other thread: Pitch: Support LTO for Swift.
Overall, I think for the generator or even SwiftPM to produce some kind of manifest of dynamically linked libraries makes sense. If you're interested in fleshing out the design for it, please feel free to create a separate thread, or an issue on the generator repository.