I would say the first sign is that the sheen has worn off and people are starting to notice some deep-set flaws in the services they use. Fewer people think Google is good and never "evil", Macs don't always "just work", and Facebook continues to have "privacy issues".

You're right, he doesn't specifically give support for the idea idea we're recovering these values and capabilities.

But I think he's alluding to people, as they gain experience and perspective, becoming aware of the limits of proprietary platforms, and investigating (or rediscovering) other possibilities.

I'm honestly not seeing that people are giving up Facebook or the like because of any limits imposed by Facebook.

The worst I saw was some of the more technical minded go to Google+, which is basically the same thing all over again.

I don't think it's swinging back, but I would like to hear his reasons for claiming it is.

Twitter's original "sidebar" implementation of inline media used OEmbed, actually.