Succubi as evil demons are good and all, but gameplay cycle is getting quite predictable already, and its only first clan: you weed bunch of plants, get to new succubus, she offers you to surrender, you decline, kick her ass, she tries to seduce you before she dies, you kill her. I feel like some deviation from this blueprint would be interesting distraction. I don't insist on my suggestions, any plot twists are welcome.
As for the gameplay cycle, Zion is already aware of this. This is his first game so right now he is trying his best, unfortunately, it is true that the gameplay and the combat are a little linear. He is doing his best to improve both of these every time he releases an update, and you can see that is the case if you compare each version released so far.
Even so, the main formula you mentioned will most likely stay, at least for this game, since it fits the theme of the era that we are currently on (since succubi right now are conquerors and they are defending their territory). But even though we will stay with this main formula, we can hopefully expect:
-some side quests (like the tribal succubi and the witch quest)
-succubi that deviate from this norm (like the captured succubus)
-succubi that don't belong to the main clan of the game (like the spider succubus and IIRC, the cow succubus that will be present in chapter 3)
-love interests that don't follow the pattern that you have to die if you wish to have sex all the way (like Iole and Atessatia)
-choices that will affect the story in the future (like if you decide to side with the witch or kill her)
Exploration will be something that this game will also encourage, as some of these require you to do so in order to be able to access them. We can even see a castle close to where Drita was, which we can expect something from it in a future update. Right now, we even have the angel tower challenges for some extra content outside of just defeating succubi.