I got a few suggestions
1. Add Yuri/Lesbians and Futanari scenes.
2. Have the ability to customize the succubus
Make wear different outfits or clothing, change her butt, breasts, height, thickness or make her a futa herserlf in the options menu.
3. A school shop
A place where you can go to buy clothing, potions and other lewd stuff. purchase drinks and spike them to give to NPCs to increase their lusts and desires.
4. A money system
You can either prostitute yourself or work in the shop to make money
5. (Think is was added in the game) A diary or a logs of each individuals
Keep a special logs on all NPC's lusts and desires. The other being Logs on the player character as well.
6. Improve the Health and stamina.
Have the character find special potions or upgrades to increase both health and stamina, doing so you can preform more tasks and sex options.
Ideal suggestions but not really important
1. Have a special unused room to house tentacles, sex toys or other instruments to dominate characters
2. Customize NPC character
rather be a parent, teacher or students. change the way they act, what they do, what they like the most.
2.1 : have the ability to edited the female characters breasts and butt sizes in options menu as well.
3. Hypnotize or take over male characters and lure them away from crowd to secluded area's (Such janitors closets, bathrooms, offices, Gym's locker room.)
4. Bathroom glory holes
Have either the succubus or a female character sneak into the boys room and provide services. (Can gain money as well)
5. Day, Evening and night cycles
This will make the game more lively, that will give more scenarios and it would be better for night time classes
I know this likes a lot but think of it this way, The game will be more enjoyable for players as there will be plenty of content to play around with.
The game has potential and looking forward for updates in the future. I do hope you look over the suggestions I made and take it into consideration,