Just a random throwaway line with no intent of being foreshadowing but later it's the plot of a story.

The Simpsons Arty Ziff admits he'd give up his fortune for one night with Marge Simpson during a school reunion. A decade later, an episode plot is Arty Ziff offering to pay for surgery in exchange for a night with Marge Simpson.

Doctor Who The Doctor riffs ideas for his and Martha's next trip mentioning he'd love to meet Agatha Christie. Next season, he does by accident with Donna