I looked at my current "Next Cruise" booking. Here is one of the conditions:
5. Full Names are required at time of booking. Changes to the reservation may be permitted, subject to availability and any other restrictions and applicable cancellation charges. At least one name on the original booking must remain the same.
Looking at this, it would appear you can make a booking for someone else. But they may have other rules which don't appear on the actual booking documentation.
However, if you read the press release
about the Next Cruise option, the wording implies the program is for people who are actually on a cruise when they make the booking.