THE ONGOING CLASSIC FILM STRING CHALLENGE!!

At least with that example I think that's what he meant.  How that can be adapted for other topics into a "string" worth creating, I'm not sure.
He mentioned "Husband/Wife".  Easy to create an endless string.  Almost every star has played a spouse in some movie.  So, it's no challenge at all to keep a string going, but because there's no challenge it's not interesting either.  The thought of "Homicidal Spouses" occurred to me.  There's a lot of movies about someone who wants to kill their spouse.  But could you create a string?  I don't think so.  Let's see, Lancaster wants to kill Stanwyck (Sorry, Wrong Number), Stanwyck wants to kill Tom Powers (Double Indemnity), and....dead end.  I don't think I could string three movies with that premise.
So then "Married, With Children"?  The spouses you string must all have at least one child.  That narrows it down, and makes it more challenging. 

Maybe somebody'll think of an intriguing premise for a string.