Every CG needs to be somewhat redrawn. It looks like it actually is a lot more work than H cup - if you look at the example for the attack animation differences on the CI-EN, you can see the h-cup is basically just shrunk and clothes/nips cleaned up, where the P-cup animation, one breast is in an entirely different position.
I mean, the game was supposed to be complete after gym dlc, but here we are two additions later, one paid. Gives me hope for an official pregnancy dlc, not that I dislike the fan mod, but I feel like one from the author would be better.