We want the ability to search for both booked and proposed appointments that will or might start at a certain time.  The current date search parameter is mapped to Appointment.start.  With the introduction of the new requestedPeriod field in STU3, there is no way to search for appointments that will or might start at a certain time. Proposed appointments don't have a start date yet and only have a requestedPeriod.

Proposal: Update the existing date search parameter to qualify on appointment.start OR requestedPeriod

See https://chat.fhir.org/#narrow/stream/179166-implementers/topic/Appointment.20search.20parameter