Still trying out several path combinations, but I can say that if slutty Holly and Ian get together, there is a major fork coming for Holly.
While she certainly had fun becoming a wild girl (and likes her friends Lena/Ivy/Co.), she did so in the, partly mistaken depending how we play him, belief Ian prefers wild, slutty girls. That becomes blatantly clear by Holly´s actions and dialog in the Ian/Holly scene, her changes came to be due to the hope to have a chance with Ian one day.
Now that this has happened (by the way the hottest and partly cute scene in the update), there are several options I see how Holly develops further:
a) now being in a relationship with Ian, she stops getting sluttier and reserves her wild side for him. She got what she changed for.
b) like a, but with Ian lovingly encouraging Holly to develop her wild side a bit more to a common comfort level. Nothing big, e.g. her going topless on the beach, just a bit here and there, they are in a dedicated love relationship after all.
c) Ian and Holly recognise that they really like her slutty side and she is encouraged to develop it further a lot more.
As said I think this will depend on how we play Ian. For example, a shyer, reserved Ian will be more comfortable with a and b, while Chad Ian might prefer b or c.
By the way, Holly learned quite a bit writing fantasy books, teleporting out of her underwear! Who knows what else...