Keep in mind that a lot of your clients don't upgrade their system (for many reasons). I'm not telling you to not be always up to date with software versions, but learn to switch between different development environments that run different versions of PHP, Apache, Memcached, and so on.
Magento 2 has natively supported PHP 7 since the first release. We all agree that PHP 7 performs better; it is faster and contains a lot of new functionalities. In this case, it is logical to run the Magento extension project on PHP 7. Nevertheless, you may have some other projects that don't need this new version, or worse: they can't work with it.
We will see how to compile and run PHP 7 for the specific
vhost of your server. I will assume that your server is Debian-based, that you are the root user, and you use nginx, which has already been installed and configured.