I've noticed this warning today:
Google Maps API warning: NoApiKeys
https://developers.google.com/maps/documentation/javascript/error-messages#no-api-keys
I don't find a system setting or a plugin property to store the key.
As far as I know API keys are still not enforced, but I guess it would be a good idea to have an option to include them in the API call.
Cheers,
Patrick