SwiftPM proposals currently don't require accompanying implementation. I thought this was documented somewhere but apparently not.
I've landed much of infrastructure required for implementing resource support in SwiftPM. I've also landed this proposal (which isn't a lot of work with the infrastructure in place) so we can try it out on actual packages before fully committing on the design. If you're interested, you can try out the latest snapshot on this example package. I expect to take this proposal to formal evolution review sometime next month. @NeoNacho and I discussed this and we're ready to take this proposal to review now!