The premise of Momcest Trainer is that the mom starts up a system where the son will earn Good Boy Points for doing things like housework or doing well in school, which he then redeems by pressuring his mother into increasingly sexual acts. Each day is divided into "school", "evening", and "night" phases, though the "school" and "night" phases are probably going to be mostly used for random events.
I'd also like to implement a magical card system, where the player can collect all cards in a set to unlock a permanent effect. For example, collecting all cards in the "Nipple" set would increase the mom's breast sensitivity, and collecting all cards in the "Cum" set would make her addicted to cum. Such cards can be acquired by completing sidequests, through trading with the other (male) students, or by playing and winning a simple card battling game. My hope is that the augments these cards provide will be an engaging way for players to customize their game, and will add some replayability to the sexual acts.