Sorry, I forgot to state my main conclusion in comparing the consequences of adding "inspect.isawaitable" vs adding an API specifically for checking "isn't Awaitable, but can be used in an await expression":

    I think we should add "inspect.isawaitable()", and have it pass for *anything* that can be used in an await expression (whether that's by implementing the Awaitable protocol, or due to special casing at the interpreter level).