Long time Unified Communications watcher Dave Michels authored a presentation at the UC Summit 2016 on the entitled "Did You Get The Message?" He cites the rise of Slack (slide 13), which in many ways is Unified Communications 2.0 vs. the more traditional version. On slide 14 he compares UC 1.0 and what I am calling 2.0.
The difference in my opinion is older work teams still work in the traditional office environment and have both UC 1.0 as their primary modes of communications. That means, a PBX, desk phones, find me follow me that rings their mobile phone, video conferencing and video calling, plus internal texting. Some companies have added on Slack or Hipchat, but largely to communicate with the nerds and geeks in IT, product development and other "engineering" or "support" functions.
The companies that never had a PBX, grew up on mobile devices, had their teams texting, using Skype as a way to stay in touch, largely matured in a text, share files, and then huddle room mentality. And, if you look at the high growth tech companies most of them arrived without thinking about a UC based, PBX centric approach. That is what led to the rise of Slack, Hipchat and others, and which has spawned the new services Dave highlights in his blog post of November 23rd.
To me, the decision to go 1.0, 2.0 or take a hybrid approach in how teams communicate has more to do with how much time people need to actually talk. I would say that with Ottspot, Yodel, Zoom, GoToMeeting, UberConference, Appear.In, that voice and video are actually there in Slack, and with the ability to use RSS, Zapier integrations and more, that Slack is actually today far more unified than the newly minted "Work_____" services coming from Microsoft, Broadsoft and Mitel at this time.
Perhaps that will change and UC will then hit 3.0, but for now, enterprise scale communications is clearly divided by those that talk a lot, and those that don't.