They're focusing so much on their store now and with them adding something they once said they would never ponder about doing, paid 90's, there's really nothing stopping them from turning garrisons into yet another cash cow, cash sink. With them taking forever to release the type of resource that will be used for it I kinda fear that they will add an option to buy whatever resource is used to upgrade it and add paid upgrades and cosmetic stuff only available on the store.
I'm really excited about garrisons since they are farms on steroids. It will be a real bummer if they add yet another pay to win, pay to own while you pay to play option... More stuff added to the game that we can't obtain without paying more money in a game we pay monthly to play...