Are you sure it was supposed to provide "cover for spies"? AFAIK onion routing was an invention of the US Naval Research Laboratories and was public from the beginning. If you want "spies" to use it, you don't want them connecting to known gateways. High anonymity (simplex) is why number stations are still a thing.
They're still a thing as recently as a year or two ago when I looked into it. They're "perfect" in that the receiver can't be identified from the message or its channel (other than catching him with his radio), and that the message cannot be reversed (encoded w/ a one time pad). So they're hard to replace.
