A game's release schedule has very rarely been affected by what the modding community is working on. The only exception I can think of is when a company explicitly pulls mods to put them in an official release, since the modders are doing a better job. This also fosters community involvement, which is good for a game's lifespan.
These questions purpose were to highlight how adding new stuff increase complexity and time. I didn't suggest including mods in the game.
To simplify, if we add X costumes it would require X times more work to add new boobs size. Reason is that a costume (at least in current implementation of layers) depends on boobs, so any change to boobs requires change in all costumes.
To continue this thought, if we add whole art style, which depends on everything, from that moment everything would require twice more work.