However, wouldn't pulling a cousin thing out of DPC's ass be effectively running against this core message of the game? The message seems to be that you can create the family you lack, by caring about people who care about you, even when there's no blood ties. Having someone from the cast suddenly turn out to be MC's relative so "they have more family"... well, it just doesn't accomplish anything in this regard, and the intended message is stronger when the characters aren't actually related.
Which is why i don't think the "MC is from money" is a thing that has much legs, or is ever going to be a reveal. The MC's family from his mother's side hasn't given two shits about the MC for 19 years and counting. Short of looking for a kidney donor it'd be weird for them to suddenly change the tune.