The supposed benefit of a subscription-based service is that the consumer receives some type of regular improvement, new content, or maintenance. You, the consumer, are paying somebody to work on a product regularly and, as a result, get to enjoy the fruits of that labor. I might pay for a newspaper subscription to get new content (or new printings), Netflix to get new shows, or a cell plan to ensure the network is maintained (and expanded).

Breaking a feature on an already-sold product and then charging continuously to "maintain" a one-time unlock seems like something closer to... extortion.