Carnival here in Australia is a slightly different beast to her operations in the US, we do get the short cruises occasionally but generally the cruises are longer than 3 or 4 days, due to the distances needed to get to ports in the South Pacific.
Time will tell if that changes here and or the 2 P&O ships culture and crew will change totally or just be diluted, or even if some of the culture goes across and dilutes Carnival here.
I am hopeful that it will be somewhat of a merging.