Hi there,
Thanks so much for your interest in our plugins–happy to help clarify this for you! We’re still in the process of exploring options for adding different URL structures to our staging site validation tools, though we don’t have any new information to report at this time. I can confirm, however, that using a single license key across your staging and live environments will work just fine with WP Engine (or any other staging environment of your choice). We have a great post from one of our support team members, George, that sheds a bit more light on the subject:
https://theeventscalendar.com/support/forums/topic/licenses-on-wpengine-staging-sites/#dl_post-1217027
Hopefully these details will help to set your mind at ease a bit! Please don’t hesitate to let us know if you should have any other questions here. Cheers, and thanks again for stopping by! 🙂