At past coronations the Royal Dukes were positioned in front of the peers gathered on one side of the Theatre. So it would seem appropriate for Edward to become a Duke, and not be the odd one out, in time for a coronation.
I do add that I really don't expect to see such a body of peers and peeresses again to each side. These days those positions are more likely to be filled by worthy people representing causes and good works supported by the royals.
The diagram shows the positions in 1953 of (Philip) the Duke of Edinburgh, (Henry) the Duke of Gloucester and the current and very young Duke of Kent.