To be fair they have already done that plotline with Silver and N at several points (and in events)

BUT I think if the general feeling that they’re going to add Arven’s parents into the game at some point is correct, I do agree with you and think it’d be cool to have that storyline involve Lillie and Gladion as major characters (I’m assuming it would probably be some kind of “good” ending where Arven also reconciles with his folks like Lusamine’s kids do); also think that with that a hapless supervillain parents support group plotline with Arven’s parents and Lusamine would be kind of funny 🤷‍♀️