promised vs soon-to-be

promised

adj
  • Predicted; expected; anticipated. 

  • Under obligation to some future commitment, such as a marriage or vocation. 

  • Due to become manifest because of a past promise. 

soon-to-be

adj
  • Planned or destined to have a specified position or quality in the near future. 

How often have the words promised and soon-to-be occurred in a corpus of books? (source: Google Ngram Viewer )