Princess announced some themed cruises for this month and next. You can read the details at Themed Cruises – On Board Special Events - Princess Cruises .
To summarize, there will be 80s themed cruises this month and next on the Grand Princess (October 18 and 23) and the Regal Princess (November 29). All are either 4 or 5 days. There will be some 80s tribute bands, 80s movies on the big screen, 80s TV shows, and other items. I'll be on the November 29 sailing and hoping for a good time.
There will also be comedy-themed cruises over the next few months on the Grand Princess (October 14 and November 1) and Regal Princess (November 19 and December 9). They promise classic comedy sitcoms in the cabins (does "The Love Boat" count? It's certainly a classic!), classic comedy movies on the big screen, movie and TV trivia, and comedy-themed game shows. I haven't heard of any of the comedians they currently have listed, but I'm sure they're good.
I don't think Starvista, ECP, or Sixthman are worried, but I think it's an interesting ploy by Princess to fill up their ships. I hope it goes well for them.