Quarantine exemption already is in recent CDC language. I'd expect similar guidance on group gatherings, and maybe international flight testing requirement exemptions for US citizens first. Then, as the EU and others continue to expand their rollouts, some type of CLEAR/pre-Check system. Those in the UK may need both doses of AZ. I'd expect whatever vaccine(s) is/are approved in your country of origin to be sufficient if that comes to fruition.
Vermont changed their quarantine requirements effective today. The changes:
1) If you are fully vaccinated, and greater than 14 days out since your last dose, you no longer need to quarantine or test negative to visit the state.
2) Vermont residents who meet the same requirement do not need to quarantine upon return if they leave the state for non-essential (ie, leisure travel) purposes.
The big caveat for visitors to Vermont, though: They still can not socialize (other than outdoors) with people who are not a part of their normal immediate household. So, this means that my now fully vaccinate mother from PA can visit Vermont without a quarantine, but she can't stay with me at my house.
The big caveat for vaccinated Vermont residents: Although we don't need to quarantine after returning to the state, we may still need to quarantine upon arrival at our destination, depending on the local rules.
So probably the only thing that will really change in the near future is that elderly or health care workers from out of state can come here to ski without a quarantine. I suspect we'll be deep into mud season (ie, worst time of the year to visit) before another substantial change occurs.
I assume that if Vermont, where the COVID rules have been particularly restrictive, has loosened their requirements, than the same is probably true with other states.