probable vs soon-to-be

probable

adj
  • Likely to happen. 

  • Supporting, or giving ground for, belief, but not demonstrating. 

  • Likely or most likely to be true. 

noun
  • A person who is likely to appear or do a certain thing. 

  • Something that is likely. 

soon-to-be

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

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