Hawaii cruises from the mainland are relatively rare, and as you note RCI does them as part of a repositioning from Alaska to Australia.
Round trip from the same mainland port can't be done because of the Passenger Vessel Services Act, and given the distance involved the ship can't stop at a foreign port unless it becomes a much longer cruise. Thus you will see Princess has a few Hawaii cruises that depart from San Francisco but end in Ensenada, Mexico, to comply with the law. Years ago, when Norwegian first started their cruises that sail around Hawaii, they had to take a long diversion to the Republic Of Kiribati on each cruise since it was the nearest 'foreign' port. When the line succeeded in getting Congressional relief and U.S. flagged their ships, they no longer needed a foreign port.
RCI does have an interesting 10-night cruise to Bermuda next year on Vision Of The Seas. It is round trip from Port Everglades and stops at Bermuda, Nassau, and Coco Cay. They are doing it three times - June 9, August 18, and September 1.