Is YouTube tracking children?
YouTube collects data on all of its users. Lots of its users are younger than 13, because they like to look at screens and some of them can't read. But tracking children is a little more nefarious than what they do. They are in trouble though with the FTC for this.
Will Facebook's cryptocurrency be a success?
That is a trillion dollar question because quite literally Facebook wants to replace a huge part of the world financial system. It is off to a decent start. People still don't trust Facebook, so, complicated.
Should Slack replace email?
It should certainly replace lots of threads and lots of reply alls that you don't need to go through. There's still a lot of use for email like the long messages and thoughts.
Last. One thing: Be ready for cyber warfare. Tensions with Iran continue to escalate. One way they will retaliate, as weaker nations will do in the future against stronger nations, is through cyberattacks. So, be ready to be phished.