As others have pointed out, this doesn't work. None of the guidance advocates vaccinated and unvaccinated mingling in any numbers. There's a single exception to this, when it's vaccinated mingling with a single unvaccinated group.
Once the interactions are large, as in every single public instance where unvaccinated are present and community spread is high, recommendations are mitigation measures for everyone.
If we don't get high enough, this plan isn't going to work for them. It'll work for some small percentage, but if it's such a large number that community spread doesn't come down, there will be no coat tails to ride.
I think you're correct that vaccinated people will not put up with this forever. While I disagree with vaccine passports in general, that's the plan B as you've mentioned and the likely outcome if we don't get enough people vaccinated. It's not going to be two groups living in one world with slightly different appearances though. It's going to be the creation of two distinct worlds that occasionally interact.
Not sure if that's carrot or stick to move from one world to the other. It may really be three or four worlds. For truly public government run items, think city buses, town halls, federal buildings. They'll likely just keep mitigations so they don't deny anyone access. Private run businesses that want to be part of the Vaccinated Bubble that drop all mitigations by enforcing the bubble. Private run businesses that want to be in both worlds and continue mitigations like the government ones. Finally, private run businesses that don't enforce the bubble and don't require any mitigations. There's probably some health codes that come into play for those last two, but perhaps not. It'll be interesting to see how businesses chase customers from the different groups.
I still think (hope) we can get enough vaccinated, and continue mitigations long enough that the combined impact drives spread low enough that all mitigations can then be removed without spread returning. That we can all live in that one scenario.