About it being counterintuitive, doesn't the game already have something like that with the Minerva route? You need to be antagonistic towards her and that gets you the route.
I'd say Ian/Minerva is more of "a domme wannabe getting tables turned on her and submitting" route that's pretty clear about its nature -- afaict the game on this route doesn't provide you with any heart options that would actually result in
losing any chance at romance with Minerva when picked. At least as far as the choice icons go, the game is always consistent.
The Ian who has moved on can be more desirable as he displays maturity and a lack of desperation. As for Ian who has moved on, him making moves on Gillian could be a result of him no longer holding her cheating against him and thus just seeing it as a hookup.
"I no longer give a fuck about you" which is what true moving on boils down to isn't a display of maturity. It's just a display of what it says, that one no longer gives a fuck about the person. Losing interest and maturity are largely unrelated. It'd be then especially
immature if Ian started to try to hook up with Gillian -- the only thing he'd really achieve this way would be to make himself look like Axel Lite, so desperate he'd claim one thing but really want another. I don't see Gillian really entertaining this.
There are other instances in the game where Ian can express disinterest in a girl and later sleep with them, namely Lena and Alison.
I think it's quite different in intensity -- Ian is either given two options and focusing on one means he can't purse the other, or he can says he isn't interested, but it's far cry from explicitly selecting he wants nothing to do with the girl in question, that he has moved on and he doesn't want to think about her at all. Something the game obeys with both internal monologues and by actually removing Gillian-related content (Ian who has selected to move on doesn't get the "cheating Gillian" dream in Ch.11 as well as the earlier one, e.g.)
But just to be my own devil's advocate, on the other hand the dream Ian gets in Ch.11 if he's chosen to move on in Ch.3 has the dream Gillian talk how "It doesn't matter whose fault it was" and how she "wants to suffer together with Ian" and won't Ian please take her back. So, who knows. Guess we'll see, but i think it'd be really poor idea to effectively lie to the player about the meaning of icons which are supposed to remove ambiguity from provided options.