my admittedly NON scientific answer:
Buffets will not be operational in the traditional sense. at best, they will be cafeteria style with a crew member filling your plate with whatever you point at. they could operate as a fast casual restaurant where you order at one spot, take a seat and have your food brought out to you
MDR: the default has typically been you are seated with your own party alone on My Time Dining. they can easily extend that to traditional dining as well as remove tables that seat more than 6.
Shows: doesn't take much to block off every 3rd seat( so couples can sit together) and to stagger the placement of seats to ensure there is adequate distance between rows.
elevators are trickier, I think. can they station crew at each bank of elevators to limit how many get on? will those same crew have the ability to call an elevator on demand for those in WC/ECV/Strollers. I can't see that happening logically especially after muster, around show times and MDR times. ,maybe they will have them thoroughly cleaned and sanitized 8 times a day instead of 4. maybe they will strongly encourage the use of masks while using.
there is increasing evidence that surfaces are not as conducive to the spread of C19 as your fellow passenger. will they make say the pool deck one way Port side and the other way Starboard side? will they limit Bingo games to no more than 25 people at a go?
In my NSHO, the cruise industry can adapt, short term and long term, but it's not going to be easy and would probably turn off a fair percentage of cruisers, possibly permanently.