It doesn't scale, as the above spec points out. Pinning could be used to eliminate CAs (as most people initially expect) but this isn't viable at the moment. The specification, which proposes a method to validate the certificate chain, also accomplishes very little: it's fully vulnerable to MITM attacks on the first client connection. There are also privacy concerns about storing pinning data; and a browser which is configured to clear all data at exit would not see any benefit.

It's also wrong to say that public key pinning (which addresses PKI/TLS weaknesses) makes DNSSEC redundant. I suppose the proper comparison would be to the (optional) DANE?