I see that you like my idea. 
Well, it's a good idea if implemented safely, but I won't let you take all the credit, since I've discussed such a thing in the past:I could provide a zero knowledge proof that I am in possession of the extended private key or the seed phrase which was used to derive that private key.
On a wider scale, although it would be great to have such a thing implemented, and it would be a prerequisite to me being comfortable with some coins being "locked" by consensus, it would only serve to make a small difference in the event that quantum computers can break the ECDLP. Assuming that the majority of addresses which are being actively reused would migrate to quantum-proof addresses, and that the 1.73 million BTC in P2PK addresses will be stolen regardless, then this system would only serve to protect coins in non-reused non-P2PK addresses which are inaccessible to the owner. We cannot place an accurate figure on this group, but I believe it to be significantly smaller than all the estimates bandied about by people who simply assume that any coin which hasn't moved in >5 years (for example) has been lost, since (for example) such a category includes the majority of my coins, which are absolutely not lost.
It's certainly worth doing for the individuals it would protect, but it will make little difference I think to the overall impact on bitcoin.