I was thinking of getting it in a month or two if popularity had not started to crash, but the comparison to MTG has me suddenly convinced that I better wait and see what mojang does with the concept of expansion packs and how that is handled. Having to pay real cash every 6 months to keep up to date palls, just a bit. Even if the price goes up after release like minecraft did, I'll not regret waiting.
They've addressed that. I believe what they said was that you must buy the game, but you don't have to buy anything else in order to stay competitive. There
is an in-game currency called shards which you have to buy with real money, but I can confirm you really don't need to do that to be good at the game. It comes down to skill more than anything else.
As for expansion packs, I don't think it's really going to be able to work that way. In the shop, you can buy a random scroll from any of the three factions, a completely random set of 10 scrolls from all factions, the three preconstructed decks (you get to pick one when you start, and you can buy the other two instore if you wish) and a set of six scrolls that are "recommended for you", pretty much based on which faction most of your scrolls are from and which scrolls from that faction that you have the least of, as far as I can tell. You can't pick any card and just buy it. I just can't imagine expansion packs working that way.
In the last update, they added three scrolls, not in a pack or anything. I just don't think they'll do that kind of stupid thing, they know it's unpopular, and they are one of the game studios that cares about their players, unlike some...