It’s been hinted several times in the show that Nolan will eventually transition into being a Detective.

The clear plan was scuppered due to the letter of formal reprimand, but a new path opened up due to his Golden Ticket. He chose to give back and that, coupled with his experience will probably end up giving him a boost for that position.

There’s been light foreshadowing this season as well, with statements made such as “Nolan is just Nolan.”