I was excited to give this a try but unfortunately, we have to depend on SwiftPM's release/6.1 branch, which in turn pins us on SwiftSyntax's release/6.1. I believe that's the reason I'm not seeing a build time difference - that branch doesn't have any pre-built libraries.
Is that perhaps something that's going to be available at some point or is this only ever to cover SwiftSyntax releases? (I wish we didn't have to depend on SwiftPM but we have to at the moment.)