I think it would make sense to temporarily suspend the PVSA requirement to visit a foreign port on closed loop cruises (i.e. no real transportation involved). Leave the distant foreign port requirement in place for one way cruises. I would also like to see cruises to nowhere be allowed again.
I could see the "demand" for cruises initially being for short, close to home sailings with few or even no ports. Not having to stop at a foreign port for those sailings would also eliminate the need for those countries to be open to accepting US citizens before cruises could resume.