As much as it pains me to say it carriers will never be added for one simple reason, range. even earlier carriers will be able to launch planes carrying the equivalent of battleship shells from a range of more than 100 miles and proceed to drop them relatively accurately. This makes battleships, and battlecruisers functionally obsolete. Adding carriers will completely change the game possibly even more than real life as players will have the benefit of hindsight and build more carriers earlier.