I've thought about a cargo cruise......once I can convince someone to go with me
I'm planning a Tokyo to LA cruise in 2017 on Crystal - The Symphony is about 800 people but over 50,000 GT, so it's luxurious and not very crowded (and not too small to be bopping around in the Pacific). Last fall I took the same cruise ship on a San Diego to Auckland trip, and it was wonderful. There was a family on that cruise who were doing a 'round-the-world adventure as well (their very well-behaved kids were out of school for a year).
Crystal usually has the Symphony crossing the Pacific in one direction or the other, but sometimes it's a port-heavier cruise and sometimes it's a port-light cruise.