Google maps api key is essential now - https://www.linkedin.com/pulse/important-changes-google-maps-api-v3-website-owners-sandeep-kumar
I think all the authors of themes and plugins that use maps should be warned that since 22 June 2016, Google requires a mandatory Maps API key for maps created on NEW websites/domains.
It’s important to know that existing maps on existing websites/domains will still work WITHOUT an API key.
What this means for you as theme/plugin developer?
The maps on your item demo website (where you do not use an API key) will still work and you, as developer, will not be able to see the difference. But new buyers will buy your theme/plugin and when they install it on their website, the maps will not be displayed if they do not have the feature to enter an API key…
So if your theme/plugin does not support adding an API key, you might want to consider to update your item
This is Google’s post: https://googlegeodevelopers.blogspot.com/2016/06/building-for-scale-updates-to-google.html