Judging from the amount of items sold on the GNT already, many, many people have bought packs, and I am rather thankful for it, because I have enough time to grind dailies and buy what I want this way without gambling.
Many people also posted about buying coins already, so it's not all people who spent their accumulated coins from being a subscriber. So far, the concept seems to work - people spend money! We'll have to see if it lasts or if people get fed up/upset with the gambling aspect of it.
Btw, the mask of Nihilus sells for more than 20 millions on my server - not buying that!