Ghostbusters Reboot: 29 Easter Eggs, References & In-Jokes
26. Louis' Hat Reference
It's a major shame that Rick Moranis was the only original cast member of the first Ghostbusters movies who didn't return for a cameo, but given his extended hiatus from acting after the death of his wife, you can wholly understand. He hasn't retired though, and says he's just "picky" about what he does - which isn't exactly a ringing endorsement of the film.
Despite his absence, there is a tribute to Moranis in there, however.
When Melissa McCarthy's Abby Yates first appears in her lab, she is wearing what appears to be a more sophisticated version of the colander-like brain scanning apparatus that Egon uses to assess Louis when he is possessed by Vinz Clortho. The science has obviously improved somewhat since Egon's improvisation.