Holly almost certainly will get one more outfit if her change variable is high enough, probably similar to Ivy's or Lena's lust outfit. Holly is the only one I'm certain has one more big change coming, the question will really be how. Will she actually get a tattoo? Piercing? How will her hairstyle change? Outside of Allison dying her hair and Holly letting her hair down, instead of in that messy bun, hair styles haven't been explored as a way to update a characters silhouette. I'm hoping for another good girl outfit too, if she's dating an Ian or Lena that haven't caused her to be more like Lena.
An idea that just popped into my head that I now kind of fancy. If another round of clothes get unlocked for Ian and Lena, but is only available if they have level 10 in a stat. We're enough chapters in that at least one if not two stats can be at 10 with others not far behind.
I imagine Eva intends to at least use
some of those tattoo variables for Holly at some point, though I am curious to find out if she will have different option and what will influence them. I think it'd be interesting if she decided to get one, unless her romantic partner discouraged it, and the design would differ based on who she's with between Ian, Lena, both of them, Ivy or single-slut. That's five of those tattoo slots used at once and they could even be combined.
As for piercings I am hoping the topic comes up if and when Lena gets to explore such options again. Nipple piercings for both of them would be quite hot, but also rather daring for Holly.
I doubt her hair will change much more compared to now, I think her letting it down permanently will be it unless Eva gives her a hair colour change as with Alison. But I think her glasses might change again, or even go away completely. I don't recall if she mentions how well contacts work for her, I could imagine her going contacts only even if she has some issue with them with a high change variable because "beauty is worth suffering for" or some shit like that.
As for outfits outside the once based on her sluttier routes I'd be thrilled if she could have one unique to low change romance with Lena and perhaps some options if she's with both Ian and Lena, that would really set her apart visually.