There's no reason whatsoever that Ian can't do hard porn further on in the game - unless Eva doesn't want that. It'll probably just take some time to get to that point.
It seems Ian starts off with a more normal/less extreme view of sex due to having been in a long-term relationship with Gillian, which probably didn't allow for too much exploration (although apparently he was really good in bed because, iirc, Gillian told Allison enough about her sex life with Ian to leave Allison wanting to experience it herself). However, after Ian gets over Gillian enough to see other women, and really gets into the sex, we see the options for a more dominant personality coming out during sex (if the player chooses those options).
Considering Lena is getting some sort of degeneration/transformation path, it stands to reason that Ian will too - and as I said, there are already indications of it. It wouldn't make sense for only one of the MC's to have a transformation path while the other stays the same, especially in a game where both MC's are given equal shares of the story. For Ian this may be further helped along by a closer friendship with Axel and Jeremy, and choosing to move further from Perry and Wade. His involvement with Seymour may also nurture the more ruthless/dominant side to him.