they actually have to reference the function by string name.

This is true of a lot of the opt-in language features though, isn't it? For example, you can just make an .Add method on any IEnumerable type and get collection initializer syntax supported for it, even as an extension method. The same works for Dispose on ref structs I believe, and I remember there being a few other places where this was true (GetAwaiter I think?).