Stunt Casting: Done an awful lot within a couple years — it seemed like pretty much every high-profile gay-friendly celebrity in Hollywood was doing one-shots on the show. Madonna, Cher, Jennifer Lopez, etc.
What Could Have Been: There were plans for a Jack And Karen spin-off, but after Friends spin-off Joey got cancelled, the creators wisely decided against the idea.
Jack does some Leaning on the Fourth Wall as he wonders aloud if maybe people somewhere are watching their lives unfold. Karen dismisses the idea because a Jack and Karen show would be "good for poops and giggles, but it would never last."
Although, Megan Mullally talked for a little while in 2009 about a Karen Walker musical on Broadway. She said it might feature Leslie Jordan as Karen's verbal sparring partner Beverly Leslie. However, she claimed it was being written and composed, but not much else has materialized.