The answer could be really simple.
1. PS Now will not be a subscription service in the way where you get access to all titles by subscription.
2. The subscription (if one is even needed) will simply allow you to play games you have digitally purchased on the playstation store on any device that Sony enables.
The question, then, is, will Sony allow free use of PS Now and simply charge by making you purchase the games from the PS store? If so, there would be no subscription fee at all and their increased profits would come from increased digital game sales and increased audience due to the ability to use any device that they allow to connect to PS Now. Not to mention, the ability to allow backwards compatibility with any console they produce, PS4 or any in the future.
They could also simply require you have PS+, which would undoubably increase the number of subscriptions while allowing people with PS+ on a PS4 to play all their free PS3 games.
