Now, PHP 7.0 will reached the end of its critical support through December 2018. After that date PHP community will no longer provides support for bugs. Following to PHP 7.0, PHP 7.1 will be put under discontinued support next year.
With recent updates, WordPress has increased it server requirement from PHP 5.6 to PHP 7. I think it is the best time to upgrade PHP to follow the requirement. FYI, Most of my servers are running based on Debian Jessie.
In WordPres 4.5, my old function to add a custom size to media uploader seems not working anymore. But I found that new way to add custom size image is a lot simpler using image_size_names_choose filter.
Basically when you create your own image sizes using the add_image_size function: