So you don't care what happens to peoples' bitcoin who choose not to move to this new address type? I don't think that's a reasonable solution to require people to send their bitcoin to a new address type to avoid losing their funds. That's not the same as segwit or taproot as people had a choice and the default action (none) did not have an adverse affect on them. You didn't answer the question either.
Well, that's a completely separate debate. If the time comes that the ECDLP is broken by quantum computer and we can no longer rely on elliptic curve cryptography, then bitcoin will and must fork to some quantum resistant algorithm.
The question you are posing is how to go about doing that. Saying that you don't think it's reasonable to expect people to send their bitcoin to a new address type is missing the point - if ECDLP is broken, then all current addresses are vulnerable. We can't make ECDLP magically secure again and let people continue to use their current addresses.
The only option is to introduce a new quantum resistant address type and have give everybody plenty of time to move across to it (in the order of several years). What happens with coins that don't move becomes the real issue here - do we either decide as a community to permanently lock them* so they can never be moved again, or do we just ignore them and let them be stolen by whoever manages to first and then re-enter the general circulation. I am in favor of the latter option.
*Perhaps the best option, but one which would need a lot more work to be viable, would be to lock all these coins but provide a mechanism to unlock them if the real owner can provide some quantum-resistant proof that they are indeed the real owner. An example would be if I could prove that I owned the seed phrase which generated a given wallet or address. Such a mechanism (if developed) would only solve the issues for seed phrase generated address though, and there are a lot of vulnerable coins in P2PK address that this does not address.