I feel like these are going to be very close to the rules once cruising is allowed to expand back to the US, with a few caveats
Vaccinations - This is the biggest unknown still. I feel that
DCL is requiring this due to UK laws/guidelines. This is such a touchy subject in the US, but if the CDC were to say they are required, then this would remain. If any ports require them, then it will remain. Otherwise, they may fall back to vaccine OR negative test. Not sure how I feel about that yet. I'd much rather they require vaccinations, at least for the first 3-6 months of cruising.