In fairness, aside from whining about the minority attitude towards NAT [0] the person you're replying to absolutely met your definition of "gratuitous":

  (i.e. anything other than the decision to make a breaking change to address formats and accordingly require adapters)

I (and I expect the fellow you're replying to) believe that if you're going to have to rework ARP to support 128-bit addresses, you might as well come up with a new protocol that fixes things you think are bad about ARP.

And if the fellow you're replying to doesn't know that broadcast is another name for "all-hosts multicast", then he needs to read a bit more.

[0] Several purity-minded fools wanted to pretend that IPv6 NAT wasn't going to exist. That doesn't mean that IPv6 doesn't support NAT... NAT is and has always been a function of the packet mangling done by a router that sits between you and your conversation partner.