When E+ was first introduced, it seemed that the middle seat was often left open. Now it is rare that the middle seat is left open. UA tends to use smaller aircraft on its long-haul and the middle seat is often filled with stand bys who have no status.

On more than a few occasions the person boards in the last few minutes and is excited that they got E+.

If it becomes truly a separate cabin, I wonder if this practice would continue.