I cannot imagine having the time or money to do a cruise of that length. And frankly, as much as I love cruising I don't know if I would like a world cruise. Two weeks would be my top, maybe three weeks. I doubt I could be isolated from home for much longer.
Perhaps this is due to my having done two back-to-back 6-month Med cruises in the Navy plus "many" one to two month cruises here and there. These gave rise to the acronym NAVY....Never Again Volunteer Yourself!