Without being qualified to judge the necessity of making this a language feature instead of a library, I’ll add my concurrence with Jordan’s general philosophy here: Swift should, when possible, prefer adding language features to make a thing possible over adding that thing to the language directly.
I thought SwiftUI was an excellent model for this approach: property wrappers and function builders are finding excellent uses well beyond SwiftUI, even though SwiftUI was the star client for them.
If distributed actors do in fact need new features in the language itself, it’s perhaps worth a design pass to consider whether smaller, more composable language features might serve those unmet needs.