This isn't necessarily an Easter egg, per se, since Loomis is mentioned explicitly a few times by the podcasters eager to speak with Michael and by his new doctor, Dr. Sartain. But one mention of the OG doctor earned a big laugh at my screening of the film: Laurie is introduced to Sartain by the police after the doctor survives Michael's bus crash, which is when he takes the opportunity to mansplain her trauma and convince her Michael deserves a second chance. "You must be the new Loomis," she says, rolling her eyes and barely hiding her disdain.
There are other ties to Loomis's experiences with Michael, especially the way he preferred to describe the killer — "pure evil." There's even a recording of the old doctor's voice giving a statement in court that Michael should be given the death penalty rather than be allowed to live in a psychiatric hospital.