I disagree that we should be standardizing language features that have not been implemented.
I think having an implementation is important because:
1. the act of implementing a feature forces you to work out details that you may not have thought of ahead of time. For example, for a small syntactic extension, the implementation would have to work out how to fit it in the grammar, and how to present the new feature in, say, error messages.
2. having an implementation allows users to try out the extension and gain some empirical evidence that the extension is actually useful in practice (this is hard to quantify, I know, but it is even harder if you can't even use the extension at all).
If some feature ends up being particularly useful, it could always be standardized in the next iteration of the language, when we've gained some experience using it in practice.
-Iavor