Research firm IHS Electronics and Media estimates that subscriptions to the PlayStation Plus premium online service for PS3 and PS4 will generate $1.2 billion for Sony by 2017. IHS estimates that Sony brought in $140 million from PS Plus subscriptions in 2012. Obviously one of the biggest reasons that subscriptions will grow is because - starting with the PS4 - playing some online games will require having a PS Plus subscription.
To its credit, Sony has been careful not to put all online services behind this pay wall; for example, you can still record and share gameplay video with friends, and watch entertainment services like Netflix without a PS Plus subscription.
"IHS believes that lower research and development costs for PlayStation 4 hardware, additional revenue streams from online service subscriptions and a more aggressive transition to higher margin digital content sales are combining to strengthen Sony's games business outlook even in the face of increased competition from cheap Android consoles and alternative devices eating into consumers' gaming time, including smartphones and tablets," suggested the research firm.
I guess we will have to wait until 2017 to see if the firm's estimates are correct.