Should be noted I can use NSGlassEffectView perfectly fine. It's just any new SwiftUI symbols that crash immediately.

They would be in a specific directory, something like what you suggested in Library/Application Support/MyApp/Folder. We are not going to support these packages being created by third-party developers it would just be a mechanism to slim app size. These are code language support bundles, so we'd also be allowing users to only download language features for languages they use.