Somebody should fork PHP 5.6. There is a lot of Software still depending on it and it is unrealistic to expect companies to migrate millions of lines of third party code to PHP 7.
PHP 7's changes shouldn't affect most 5.6 code, and the code that is affected should not be difficult to fix. It's not supposed to be a Python 2/3 situation.
Another problem are the Docker images. The PHP project still provides Docker Images for 5.6, however to my knowledge they are not updated anymore (perhaps I'm wrong). So what about all the security vulnerabilities in the underlying linux image? (I just verified and the latest php 5.6 image is from January 2019)