FWIW, it looks like there's been some recent (this year) work done in this area in the compiler, behind underscore-prefixed features:
You can write #if canImport(ModuleName, _version: 1.2.3) where the version is compared against a value baked into the .swiftmodule file using the -user-module-version flag when it was compiled (example).
There's also support for checking the version of Clang modules using _underlyingVersion instead of _version, but it looks like that checks the version number in the .tbd file, which isn't as obvious/user-friendly as the SDK version number (example).
So that work seems like it would be an interesting jumping-off point for discussion, as well.