Earlier quoted context omitted.
Who says you have to maintain old code? We're talking about simply not deleting it and establishing a discrete semantic for the new version as truthfully, a new version is new content which demands a new name to accurately and precisely describe it. If it didn't it would be like saying different content doesn't produce a different hash.
Except that naming things is one of the hard problems. I don't see why a major version bump can't be considered a different library. I guess you can use version numbers in the name instead, since this talk is specifically targeting maven artifacts.
Hickey's other talk says hard is relative, and I happen to agree, especially when it comes to naming. The question is to what degree of exactness you can confirm what exists (in problems). That is a function of your degree of truthfulness. So it's "hard" only in the sense it's hard to approach 100% truthfulness. However, I have observed that one doesn't need 100%, one needs to be beyond a certain threshold of effective sufficiency. And according to human history, special, rare individuals are born who do exceed that threshold.