I think it's impossible to predict what will happen in the tech world, much less when. But I don't think that it will be any secret when change happens. When the first Palm Pilot came out, there was massive coverage of the device in all media because everyone recognized that it had changed the landscape.
The same is true when the iPhone came out - there was a lot of coverage of the new, fairly expensive phone. A lot of people liked it. And a lot of people didn't think it would succeed, often because they didn't believe that people would either pay for the phone or pay for the more expensive data plans. Similarly, there were still a lot of people who insisted that users...later amended to business users...wouldn't use a phone that didn't have a keyboard.
But regardless of whether people thought it would succeed or not, everyone recognized it as a challenge to the status quo. And I think that will also be the case with the next paradigm, too - because it will be so different from what came before, everyone will talk about it. Including people who don't think that the next development - which may be a slug that you put in your ear and that crawls to your brain and acts as a phone that you can access with your thoughts - will be better than touchscreen phones.
The trick for Apple and Google is to be able to recognize the next disruptive technology and jump on it before upstart companies can. Even if by doing that you are somehow temporarily tramping on your existing business model. (I.e., it would have been easy for Apple to decide against producing a phone because it would eat into their iPod business (which it has), or to avoid producing a tablet because it would eat into their laptop market (which it probably also has, to a lesser degree.)
But that's easier said that done, as the companies will need to know when to jump on the BrainSlug(tm) Phone, but will also need to know not to jump on the hundred other technologies that seem like they might be disruptive but will ultimately turn out to be a flash in the pan. (The SmellPhone...)