Examples of such properties:

• isLeapYear, weekOfYear, dayOfWeek, daysInMonth, daysInYear (currently ISO-based computed properties on Temporal.Date)
• yearType (such as "kesidran", "chaser", "maleh" in the Hebrew calendar)
• Possibly other interesting Calendar-specific computed properties

I suggested the following possible change, creating a new object for accessing these properties (name bikeshedding aside):

// Current
d.weekOfYear
d.isLeapYear

// New
d.dateProperties.weekOfYear
d.dateProperties.isLeapYear