Texting
It's like 1995 all over again. Remember when we used to have pagers and would send messages using numbers? That evolved into SMS texting, which evolved into Twitter, which evolved into lots of stuff, and now ... we have texting again.
Everything not so old is new again.
One could argue that 2014 or 2015 was the year of the Text. I would argue that 2016 will be the year that companies and marketers actually learned how to make use of text messages and texting platforms in non-spammy ways. In spammy ways, too, of course. That's always gonna happen.
Texting is more personal and immediate than most other forms of social media. And with all the new texting platforms, most of the old technical requirements are a thing of the past. The companies that begin to figure out how to use text without being disruptive or pushy will win the day.