I realize that she won't be a "true" member of the elite society (all I can think of is Sunflash and Skarlath trying to become Abbot of Redwall), but I still think she loses a lot of character by making her a part of it - even one that isn't fully compatible.
On the Fields of Justice, because of her status Quinn won't be wearing the armor or outfit she wore before she tracked down the assassin; because of her status she won't be saying the same things she might have before she became an elite; because of her status she won't be treated the same as she would have before she tracked down the assassin.
Her culture and customs and lifestyle outside of the Fields are no longer going to be those of a member of the lower class. The way Demacia seems to be set-up, she won't be able to ever act like a lower-class citizen again, nor will she be treated like one. She won't be able to interact with the lower class without being given the respect her new position requires.
You haven't changed who Quinn is on the inside, but you've thrown away the opportunity to really investigate the lower class of Demacia with this champion because she's no longer part of it. Any kind of look into the lower class of Demacia through Quinn is now distorted by her elite status - corrupted would be a good word for it. The same way that viewing Hobbit society through the eyes of Gandalf is inherently tainted because he's simply not one of them, viewing the 99% of Demacian society is tainted now as well.
Edit: I realize I probably seem angry, but I'm really just disappointed. Like I said, the 10 Demacian-centric champions are all already upper class. Their dress, their lore, their place in society is going to be similar. Unless Quinn "falls" from the upper echelon of society, any future lore and any canon armor/uniform/outfit styling is going to be that same upper class we've already seen 10 times before.
Back on topic with that in mind: I do understand what you're saying, but I believe Quinn will present several interesting opportunities to explore Demacian society. She's essentially caught in the middle--she's managed to rise above her common birth, but she doesn't truly belong among the elite (and she'll have a hard time actively trying to fit in the right way, though she may be urged by the more traditional around her). We'll still get some of that contrast--the common life vs. the life of the Demacian elite--even if it isn't in the exact flavor you're looking for.
|because of her status she won't be saying the same things she might have before she became an elite|
Beyond what's in-game, though, I've never perceived Quinn to be the type to "change herself" depending on her societal position. Outside her relationship with Valor, she's very cut-and-dry with people, to the point, all business. She was like this as a commoner and she'll remain that way as a soldier.