Many websites make use of calendar subscription options.  May I suggest the NXT setup the same scenario?  The idea would be to allow NXT to manage its own calendar.  However, allow users to subscribe to the calendar in whatever format the choose (isc, Ical, Outlook, gmail, etc.).  Let the calendar take care of syncing it.  Many sports sites make use of this option, so much so, my guess is there are pre-build web applets that can be integrated seamlessly with NXT.  Not sure if it can be tied to offer reminders or tasks or not (probably not).  

My Outlook calendar currently has subscription to 4 different sports calendars that all automatically sync and all work perfectly.