I highly doubt the PSN for PS4 will be pay to play. Considering MS is the only one charging for online gaming (minus some MMO's on PC) and still other game companies see a profit, MS is the exception not the rule. In fact, all the things that Sony has put in place for the PS3 has started to pay off, as they have been beating the 360 every week since the launch of the Slim. So I would imagine that they will keep with the play for free model, with premium content on PSN for a subscription.
I love how some forget that the PSN makes money as well. And not just from costumers' purchases, but from the game companies. Whenever they want to put out a demo or game on the PSN, Sony charges them for the bandwith to do so. So it's all being paid for. In fact, I believe that PSN has more dedicated servers than Live.
Sony plans to be profitable starting in 2010, and I definitely believe they can do it.
