There have been questions regarding trading cards with the game, namely on this forum post. This is but a little heads-up attempting to clear up the confusion.
Long story short, trading cards and related goodies have already been made, but due to the abuse of some users, new confidence metrics have been enforced by Valve, and this game has yet to achieve them.
As you might expect, said metrics remain undisclosed, to avoid being easily surpassed by "fake" developers. (People who had a game that sold 100 copies but had tens of thousands of keys distributed) At least, that is the terminology used by Valve themselves. You can read in full detail on their official post.
Strickly speaking, a game must reach a certain given of sales, reviews, user activity (play hours, posts, etc.), but then again, the condifence metrics remain secret to avoid being exploited.
Meaning that in the case of this game, modest in sales, but lacking in other metrics such as reviews, cards have yet to be enabled. However, please note that the day the green light is given to distribute cards. That same day, all current owners will get them. So if trading cards are the dealbreaker for you, don't worry, the game WILL have them.