I did end up calling the preschool to talk to them about DS's class placement. I didn't push for a switch, but I just wanted reassurance that he wasn't placed in that class by mistake since the school makes such a big effort in placing kids with their friends. The interim director said she didn't realize DS would not have any friends in his class next year and offered him a spot in the class with his 2 friends. yay!
Re: Update to DS's 4 yo class placement