I've been hearing about this new option for managing your upgrade where you can choose to upgrade to only an aisle or window seat for Comfort Plus. I fly quite a bit but have yet to see this option... until today. I saw this for my flight tomorrow and immediately clicked aisle or window only. I went through all my other upcoming trips and didn't see that same option for upgrading to comfort plus. Is there a definite answer on with this will become a standard options on upgrades or is it just a very random thing that pops up for certain trips? Is there any rhyme or reason to when this option should appear or is it just luck of the draw?