Steam announced support for subscription plans today, allowing publishers and players to use the revenue model through its service. The new model promises easy management of your subscription-based games, with Darkfall: Unholy Wars serving as the debut title to use the service.
According to the Steam subscriptions page, you can't freeze a subscription, but you can easily cancel and renew lapsed subscriptions in your account details. You don't get any credit back for unused subscription time, though, and whether or not you get your old game info back from a lapsed subscription will depend on the game. You also can't gift subscriptions "at this time," and you can't use multiple subscriptions for the same game on a single Steam account.