Valve has announced that it will now be adding subscription plans to its services. You will soon be able to get games that require a subscription through Steam. Users can now manage payments for subscription based games through Steam and download the games right there.
The first title they have launched for this will be Darkfall: Unholy Wars. Gamers can get their hands on the game and then be billed an additional $15 every 30 days after, until they unsubscribe.
Additional subscription-based games will follow, according to Valve. If the big names such as WoW are going to follow is unknown, but now that Steam is going in that direction it would make sense.