It seems the purpose of this proposal is to have a way to essentially have custom string interpolation. I don't think that's necessarily a bad idea on its own,

It seems the purpose of this proposal is to have a way to essentially have custom string interpolation. I don't think that's necessarily a bad idea on its own, but this syntax feels out of place to me. Instead, why not add a single new string prefix, like "l" for "lazy"? So, f"hello {name}" would immediately format it while l"hello {name}" would produce an object which contains a template and the captured variables. Then their example would be called like: greet(l"hello {name}").