There's nothing more satisfying than having calendar templates that actually integrate with most common calendar formats (at least google calendar or Apple iCloud Calendar).
Some awesome functionality:I would like to DRAW the length of an event and have that correspond to the assigned duration of the event, have Apple Calendar display my written notes on the calendar (similarly to how Apple Notes does it), have some advanced notational features that translate into editing notes or stuff in the calendar.

Or at least have a weekly or monthly planner template that also allows some "add to calendar" functionality or "get a reminder" functionality, or any such integration that would make the written planner slightly more alive.