Herrmann is looking pretty serious in the promo photos, which leads me to wonder if he could change positions at Firehouse 51 too.
While Casey is the highest-ranking officer and Severide has seniority over everybody except Casey, Herrmann could make the most sense from a show perspective.
Would it make sense in the real world for Herrmann to get the job over Casey and Severide?
His promotion would open the lieutenant’s position on Engine, conveniently right after Stella passed her exam and needs an open slot.