Then there is the discussion around how long it will take hosts to make PHP7 available and when projects like WordPress will up their minimum requirements.
For WordPress the math is something like: current PHP 5.2.4 minimum + PHP 5.4 being the most used version + PHP 7 scheduled to be EOL’d in December 2018 + the large performance improvements in PHP7. It’s tempting to pick a future date, then scream it from the roof tops so everyone knows it is coming.
My wishful thinking date for WordPress to move the minimum requirement to PHP7 is June 2017. If I were to guess though, it will be more like January 2020.