+1 for this.
I started wondering about this a while ago when we were discussing removing the Playground Quicklook APIs from the standard library (SE-0198 — Playground QuickLook API Revamp).
I gather that with this solution, we should be able to generate a swiftInterface containing the Playground Quicklook types/protocols, which would be available at compile-time in all contexts (regardless of whether your environment actually has an implementation of the framework available to load at runtime).