I would have thought so too, but then someone here revealed the mechanics inside Jean's stats, which are different from anything. As bmab mentioned, Storm's dialogues are different from the ones form before
And then there are the mechanics we never noticed. Like the one that, with good enough stats among the girl and the teacher, if the girl "offers to study biology" mid-class and you blocked Xavier with her already the teacher may start masturbating on the side...
As I said, each new girl seems to add some new mechanic for testing too. So while I'm sure he is farming it as much as he can, we can't say he isn't using it as the sandbox testing bed he claimed either.
Boss, I think he meant what they already brought.
As mentioned, Jean and Emma are obvious.
Jean has a different stats system, making her UI untrustworthy but also making her more challenging. I think it would be nice with something similar without the untrustworthy AI.
Emma has an unlock system, and her inhibition is mad high because she is a teacher. She will always try to hold back even with max inhibition.
bmab mentioned how Storm's dialogue is different, allowing it to loop instead of being a straight line.
Rogue I think we may skip because she is the source... but on the other hand, I like to think she is the one that created the addiction mechanic that later became part of the MC's power base instead of something hers.
Kitty added... being more than just one girl. So probably different ways to progress on each stat. Not on Jean levels, but different tastes at least.
Also, unlike Rogue she needs an item to blackmail Xavier. That may be it.
Laura... I have no idea, really. When I started playing she was already there.
She is more experienced, so I imagine she may have added threesomes? Or were those already there with Kitty? If not that I have no idea.
My guess about Jubilee is...
Well, in the pics we saw she got vampire fangs, so maybe she teacher the player to transfer energy? So if a girl is out of stamina he can transfer some of his (basically a sperm shot for a girl's stamina recharge)