i like the idea, that would be awesome, e.g. as a constant within wp-config.php, so that it could be configured for all sites in a multisite installation.
the plugin works great, but if you ever need to change the key, you will have to search for alle map-blocks and change the key. therefore a central place to change the key would save a lot of work.
also, after adding my own key, the message keeps telling me that i need to create my own key, this can be quite confusing, especially for users who are not that familiar with that kind of things.
