In the third episode of Sailor Moon Crystal, the one where we first meet Rei, we also get to see two old time characters. In a screenshot shown below, you can see two characters looking in a shop’s window. The two characters look very similar to Unazuki Furuhata, Motoki’s younger sister, and Reika Nishimura, Motoki’s girlfriend.
Both of these characters appear in a number of episodes of the old anime and throughout the manga. This small little appearance by them may possibly mean they will appear in episodes in the future. By any means, it means we should be on the lookout for other little easter eggs like this in upcoming episodes.