Opposite words for retrospective:
future, prospective, potential, likely.
Usage samples:
  1. And to the last retrospective of us our dead past yet speaks at times, and speaks as one having authority.
    "The Danvers Jewels, and Sir Charles Danvers", Mary Cholmondeley.
  2. When you look back on it all now in a kind of retrospective arrangement.
    "Ulysses", James Joyce.
  3. But as something retrospective, speculative, I believe it would make a hit.
    "A Hazard of New Fortunes", William Dean Howells.
  4. But statutes which merely alter the procedure, if they are in themselves good statutes, ought to be retrospective.
    "The History of England from the Accession of James II. Volume 5 (of 5)", Thomas Babington Macaulay.