She's been there since the start on the previous banner, so this isn't new.
And no, he's never said she's a "new LI", nor is he likely to either. Quinn is not going to be a LI, she simply gets that prominence on the banner because she's an important character in the story, probably
the most important outside of the 5 main LIs, as she's the driving force behind what is sure to be the main story arc of this game.
If anything, there may be an ending for her but only in the event that the MC doesn't get with any of the main LIs, and they've done certain things with Quinn, and they're a certain affinity. But even then, this will likely be painted as the "bad" ending because some bad stuff will probably happen which makes her the last person left who'll give him the time of day.