Thanks for reply.
I will think about problems your mentioned about. And I'm ready to help in implemention of new version of the package.
I still playing with current version of the Calendar and need few extra days to get an exact pciture of what I like to change. Will come back to forum with new ideas soon.
At the moment I have suggestion about item_type. I think calendar_id may be removed from the cal_item_types table.
Different calendars may has events of the same type.