I think there basically be soft-fork with dual signature types the Quantum addresses and the regular addresses for a long time.

And slowly people will slowly give economic preference to the new Quantum addresses. And that's it. To the point that people on older addresses start losing economic opportunity.

Nobody is forced to do anything. There will be a new alternative/upgrade, people will choose it or not.

It's really not that of a big deal. And it'a all voluntaryist.