Yes, in that case a Leecher(or mistborn) who was also a Chromium ferring(or full feruchemist) could write a prophecy if the other conditions were met (not focused on the now, but genuinely interested in the well being of those to come: I think you are underestimating how rare that would be). However, Feruchemy is not of Ruin, or Preservation, but of both, thus, prophecy would be a power requiring two shards: very powerful indeed. (I don't know if Sazed is still a feruchemist, after becoming both Shards. Arguably, Vin was no longer an allomancer when she became Preservation. But it might be a moot point, since one ceases to crawl once one can run.)
All that being said, I want to emphasize, this would NOT be seeing the future. To say that it was would be like saying that throwing a basketball over a house and happening to make a basket is the same as seeing the basket through the house. They might have similar outcomes, but they are, in fact, different abilities. (Look at Mat's luck in The Wheel of Time. He has almost prophetic abilities, at times, and it works to his best interest and towards his personal, deep seated goals, even when he doesn't see how in the moment.)
To that end, simply being able to see possible futures would not make you capable of writing a good prophecy, which would help accomplish your goals. Again, these would be different abilities.