Little to no posibility without paying whatever the cost difference between the two. They will continue selling balconies even if they have to lower rates to fill them. It would not be unusual for you to be upgraded to a higher than Cat4A, Riviera Deck inside cabin. To go from an inside to even an oceanview is very rare. On a June sailing date (peak season), the ship will sail full and probably sell out at least a couple of weeks at the lateset before the sailing date. If it doesn't they'll lower the balcony rate. Then you could pay a smaller difference to move up.