We don't know whether Heirlooms replace all of the starting Coppers, or just some of them. We don't know if they'll all be identical or all unique, or something in-between. I think 7 uniques would be a bit much, making it less accessible, and longer to set up IRL.
My speculation is that they're coppers with on-trash bonuses/penalties. That way, like shelters they don't mess with the opening, but can have a minor effect later on. Also, if Nocturne truly is a sequel to Dark Ages, trashing is kind of a theme there. If they're worth VP, that's kind of like a trashing penalty.