Calendar Start Date / Reservation Date

We have many events that require advance reservations, but there is really no defined way in a calendar asset to display the RSVP date. We can use a RSVP flag - but it doesn't provide the RSVP date. We can add the RSVP date in the copy, but it is lost and events are displayed based off of the start time.

Are there any suggestion as to how events that have RSVP dates can be handled?

It would be great if there was some way to have a field of data for an RSVP date - and if this field of data was filled in this date would display in place of the actual event start date.