We've had rumors about a "Share" button on the new controller. I'm sure the new "user experience" will be about a social ecosystem and nothing to do with motion controls. For a long time I've been predicting that PS4 and Xbox 720 would have OS level live-streaming of gameplay. I think they're going to make it easy to instantly share videos, streams and screenshots of what you're playing on PSN, Facebook and Twitter, AND they're gonna make it easy for friends to peak in on your game ala OnLive's game browsing capabilities. This will probably involve some of GaiKai's tech. Think of a Google Hangout where you can create a cross-game party to chat, video chat, and also see exactly what each of your friends is doing in game at that moment. Maybe with an instant replay feature so if something crazy happens in one person's game we can all pause, shift over to his screen and watch a slow motion replay of whatever just happened.
A lot of speculation about the Gaikai acquisition keyed in on existing business models and how Sony could use that. Maybe they just wanted Gaikai to form the backbone of something new so they could go above and beyond the features that would have been possible if they just partnered with Twitch, NicoNico or YouTube (but maintaining the ability to publish to those services as well.