I request the ability to swap schedules with another aircraft. This would save the time and hassle of doing it by clearing schedules and moving aircraft schedules.
This would mainly be for changing aircraft on a route due to maintenance, changing configurations, or other aircraft related functions.
NOTE: This would be only for within the same fleet of aircraft, though adding the feature for swapping between comparable aircraft fleets would also be amazing.
EDIT: This would also be very handy for market load adaptations as time progresses. Swapping between a B737 and B739 could have a tremendous effect on load factors for the routes involved.