They've updated the Known Issues thread again cause of all the confusion over DoTA2, lol.
Al also made a post over the weekend that made it pretty clear they don't see an issue with the limited drop rate. They think it won't be a problem because people will trade other items (tf2 drops, dota 2 drops, coupons, games, etc...) for cards, some people just won't care about badges, and as they add other games to the system you can trade those cards for the ones you really want. The kind of feedback they want is what other drops you want to see for your profile and is there any other community items they could create to hand out those drops.