Please no.
I'm horrified by how Valve handled the thing, creating a submarket for the cards, the emoticons, the skins of the games, with microtransactions that only serve to further fatten Gabe.
Cards that have to be farmed by spending hours playing and that are obtained by "luck", and also you can never get all of them and you have to buy the rest with real money. No thanks.
In fact I've always wondered why nobody has ever complained about this horrible practice, it's the worst of the worst of the microtransactions.
Obviously I would agree if GOG implemented its user friendly system, based on the actual ability of a player and his commitment to a particular game, cutting out all the microtransactions that are completely useless.
But I would prefer even more if they add their own original system, such as a trophy room: each trophy is unlocked when you reach 100% of the achievements of one game. That would be very nice.