This is true, but I'd be willing to bet it could still cause issues for some transit systems where they aggregate your charges for the day. Just because they have access to more detailed information through the chip doesn't mean some developer didn't use the card number as the primary key in the database.

Previously it was mentioned about hitting fare caps, but the place where I think it would be particularly bad is those transit systems that track your in & out places. Once card X has entered at a location, they can't enter again without exiting (so it knows what fare to charge). So if person A with card number X enters and their significant other with AU card X tries to enter behind them, it might not work.

Again, this assumes that someone used the card number as the key in the database, but I'm also certain there is a system out there where this at least WAS a problem at some point.