I have a multi-site-installation that is set up with the Virtual Domains component, On a Joomla 3.7 / PHP7 environment.. Is JoomSEF working in such an environment?
unfortunately question about next JoomSEF developing is still open, so I am not able to answer you now.
As regards installation - JoomSEF license is binded to the registered domain and you can register one testing and one production URL: