So the only difference would be that the chips are a less expensive way of achieving what could also be achieved trough keeping physical notes on who sends mail to who.
Personally, I don't think it will damage privacy too much, mostly because privacy for mail is practically non-existant already. (except for actual content of envelope or package, of course)
By the way, did the Pirate Party actually say anything about this? If there's an article in english about it, I'd take a look.