A question about the ending...

I knew nothing about Blade Runner before going in, so I watched it today and really enjoyed it. I was confused about the unicorn at the end of the movie. My initial question about the ending was whether it was that the origami was a threat that they would be hunted down, or if he let them live.
As I did research on this, I found that it may be linked with Deckard being a replicant. Now, I saw the unicorn scene, but I wasn't sure what significance it had, and still didn't when I saw the piece at the end. I'm not sure if this was a thing people pick up on their first viewing, but for some reason I didn't connect the dots. The only time I had a question about the replicant thing, was when Rachel asked if he had taken the test himself before, which got me wondering.

My question is, what is the most widely accepted theory of the ending? (Without 2049 spoilers). Is the replicant angle meant to be picked up on first viewing or after multiple, and is there even an answer, or is it meant to be ambiguous?