The proposition that it has failed due to the passage of 17 years since the first RFC neglects the fact that there were certain key events that inhibited adoption that didn't happen until recently:
1. The DNS Root Zone was not signed until mid-2010. As the anchor of trust for the DNS, deployment prior to this date was basically experimental. This was the commencement of production use.
2. Registries and registrars, as a whole, did not support it until recently. However, ICANN has required them to do so in the last few years so this roadblock is being removed.
The assertion that it is a failure may ultimately prove to be true, but looking at its experimental phase and declaring it as proof positive is not convincing.