Fascinating. As a native northern-US speaker, I literally had no idea how these used to work until now. (I guess most people know this, but here the sense you

Fascinating. As a native northern-US speaker, I literally had no idea how these used to work until now. (I guess most people know this, but here the sense you mentioned is the only one acceptable in speech; otherwise, "shall" sounds more commanding than "will" but archaic; and "should" always means "ought to".)