3.8.1.2 Category property in (RFC5545) is a basic and easily implementable feature, adding this will reduce the number of seperate calendars needed, also visibility dependent on category within a single calendar will be highly productive

Following the ICS spec is important to all those users that sync between devices. Some of the suggestions are misinterpreting the concept of CATEGORY and STATUS as compared to the ICS definitions. FreeBusy is NOT a CATEGORY. It is a separately defined element of an Event. Most other extensively used calendaring software based on ICS make significant use of CATEGORY and STATUS elements.