The 320s can easily have 16F as the pitch in F and E+ are above UA's current standard. It appears to me they will be adding a pair of Y seats between E+ exit rows on one side of the aircraft to keep it at 150 total for 3 FAs. We'll have to see about that configuration, but 95 Y doesn't divide by 3 evenly - thus the blank window seat at an exit is my guess.
Maybe UA had decided against changing last year since the entire fleet is being refreshed with NEXT.