I don't know that it is. Only MS have tried that, and no-one's followed. Steam doesn't charge an online fee to play your Steam games online, nor anyone else. For a subscription fee, I'd expect it to work like movie streaming - you select from the library of games and play them. An online fee like MS is somewhat like asking you to buy a BRD and BRD player and then pay to be able to play the movie. shift all the optional fancy features to subscription if you must, but a fee just to access the internet (that's pretty much all you're doing in peer-to-peer gaming) is just rude, and there are other options (Ouya, Steambox, PC).
Maybe I'm understanding it wrong then. Multiplayer-only games haven't been the norm. Most games have an offline as well as the online component. The problem I can see is that it costs money to maintain the online aspect. Sure, we could go back to the days of pure P2P gaming, but what PSN and Xbox deliver are a more or less consistent user-experience - build up a user-identity with trophies, voice-chat, chat with your buddies etc. You also get leaderboards and other features across the platform.
Now, we can argue about how much it effectively costs these multi billion companies to actually offer this as a service, but the point is, it costs money. Another problem I'm sure many game-developers/publishers are facing is that people seem happy to play what works. Why upgrade to the newer game at all if you can still keep playing the older version online for free. Most people seem to happy to "upgrade" as long as their friends upgrade so they can all play the new game together, but surely, as long as its free and having to maintain that service must be frustrating.
Now I'm not sure if paying Sony (or Microsoft) will actually help this, but at least this way, some of the money it costs to keep this service run could potentially go back to the developers. As a gamer, I would prefer paying Sony a hundred times more for a consistant service than to pay every publisher for their game seperately for "extra features" (i.e. like for Call of Duty Eite).
I'm not sure if it works like this, but if you have a pay for online service, it opens up the possibility for a better product, a better service and one way of how to give something of that money you make back to the publishers could be by asking for less royality fees for sold games on your platform (as an example).