I'd like to resurrect an old idea. Hover offers calendars on webmail which means you can only access via webmail and can't share. We are a company who has Hover host our email but we have to use iCloud to have shared calendars. We would love to have shared access to calendars on Hover on the same account as our email. Implement CalDAV and we can have that.
CalDAV support for Hover Calendars