How about a story about "Lost in Space" with a walk-on with Billy Mumy who just happens to live in the LA area? I know it's a little before your characters time, but so was the original Star Trek. You could also bring on the "Robot". Just a good idea!
How about Bernadette, Stuart and Emily meeting Sheldon's mother (Mary Cooper) and about Amy, Bernadette, Stuart and Emily meeting Leonard's mother (Beverly Hofstadter)? And Bernadette standing up to Leonard's mother?
How about Mrs. Rostenkowski (Bernadette's mother) meeting rest of the gang (Sheldon, Amy, Raj, Penny, Stuart, Emily and Leonard) with the 'Howardette' couple and Mike Rostenkowski (Bernadette's father)?
How about Howard's half-brother Josh meeting Amy, Sheldon, Emily, Stuart, Penny and Leonard for an episode request?
How about Vanessa Bennett (Sheldon's respective date) meeting the other members of the gang (Raj, Emily, Stuart, Amy, Howard, Bernadette, Leonard and Penny) as she only met Sheldon at the doorway in the "Mystery Date" episode (S9E8)?
How about a redo-wedding for Leonard and Penny and a wedding for Amy and Sheldon together in one day where Sheldon's mother (Mary Cooper), brother (George Cooper Jr.), sister (Missy Cooper), Missy's husband and their son (both unnamed), Amy's mother (Mrs. Fowler) Leonard's mother (Beverly Hofstadter), Leonard, Penny, Bernadette, Howard, Emily, Stuart and Raj will be invited to it. How about having a apartment roof for it with string quartets of 'Here Comes the Bride' in the background. How's that for an episode request?