Who cares? It's not like an invalid lookup is raising a big flag that I intend to register this domain so come on over and scalp it. Besides, there is ultimately no way to make these lookups other than plaintext.

Presumably the same people who worry about their registrars scalping them should also worry about the vast amounts of people with passivedns access scalping them.

You can make these queries via a trusted registrar, and the domains you query won’t be broadcast to the world in cleartext.