I have researched almost all the calendar plugin already. But your plugin is wonderful with great potential.
It's very simple. Simplicity is very important for WP plugins. Many popular calendar is too complicated and too fat.
It appends on any post types. It can help any post type with calendar feature.
Why don't add the feature of supporting do_shortcode feature? I think no calendar plugins are available for such features. So I can show the calendar on any template I hope.
Keep improving the plugin and I believe it will be popular.
I will keep telling you my expectations and share my ideas.