Carrier capability cannot be represented adequately by adding another hull type alone. Aircraft technology, design, and development would need their own progression alongside the ship-design system. Those air groups would then have to operate across an already very large campaign map. Adding naval aviation would create a second design system, far more involved than the game's submarine abstraction.
Notable Point · 32:31-33:08
Why aircraft carriers would greatly complicate the game
Adding carriers would require modeling aircraft design and development as well as ships, creating a much larger technical problem than submarines.