Can you explain more of what you’re looking for in terms of an import function? The purpose of ICS Calendar is to render the data from an external calendar feed; it doesn’t save or store the calendar data in the WordPress database (other than temporary caching for performance), because that’s antithetical to what it’s about, which is continuing to manage the editing of the calendar data in an external source (e.g. Google Calendar) but displaying up-to-date info from the calendar in a WordPress site.
What would you be looking to do with the imported data? Once it was imported, it would no longer be in sync with the original source. I can see the value of such a tool, but it’s not what ICS Calendar is for. (For example, The Events Calendar is a good plugin for managing calendar data within WordPress, but it has its own ways of importing data from external calendars.) Again though, the key difference is that once data is imported, e.g. into a Custom Post Type, it’s now a separate copy of that data and is no longer in sync with an external source.