Yes, a quantum adversary is theoretical, but it's catastrophic if it becomes practical.
ZKPs are an afterthought, I haven't even explored it deeply. If you have an alternative proposal for how to construct a proof of HD wallet ownership that doesn't require broadcasting the xpub globally and exposing it to quantum adversaries, I'm all ears.
FYI, accusing someone of having underhanded motives is not a great tactic for progressing constructive rational discourse.