If not already in the works, a useful feature would be an added option on the existing Project Search drop-down list (on the left side of the Project Search field) to enable a 5– or 10– item Project Search History list.
If and when enabled, the list could be accessed with perhaps an option-click or commend-click on the Project Search field that would pop–up the most recent 5– or 10– Project Searches for re-searching.
Scrivener is nothing short of astonishing! 
Thanks,
scrive