Cabbie!

I just scraped this trailer for timeline markers to get an idea of when this scene would have occurred, and this is definitely not a prequel shot. Have a look:

In the trailer, there's a hole in his sweater on the left shoulder. There's a literal spotlight on it!

We see about 10 minutes into the film, Simon doesn't have that tear in his sweater. Weirdly enough, we also see Simon has his knife sheath in the Red Void (and the rest of his clothes), but in the movie, he's naked. Obviously, the Light would have vaporized his clothes if it vaporized the SM-13 with him along with it.

These two scenes are shot so similarly. That being said, they are implied to be connected, and these are both taking place in the Red Void. Same crackling black sky. Same endless blood:

In the trailer, Simon doesn't seem so startled to be there. More resigned, like he's defiantly thinking "alright, you got what you wanted. I'm gonna fuck your entire eternity up if I can help it."

Look at the difference in expression here. He's not confused. He's not scared. He's even sneering a little bit:

There is an immense tone shift. This is leading me to believe that the trailer is actually our "post-credit" scene, and this isn't Simon's first rodeo in the Void. He's about to make his entrapment in there EVERYONE'S problem. I'd hate to be stuck in there with a pissed ghostly Simon. Yikes.

In the trailer, Simon is being directly framed by the blood tree we know he becomes at the end. The storyboard scene where Simon is shown a vision of the blood tree looks to be suspiciously like a first-person perspective of where Simon is standing. The spherical orange light at the top of the tree is poking over the trunk. I love that the top of the blood tree looks like the shape of AT-5 and an eye, as well. It's all connected imagery!

I connected this scene to a little note in one of the official storyboards...

"Something is changing in this place and Simon is witnessing it."

What changed? Well, I went back and looked... if we assume that the trailer scene truly is a "post-ending" shot, the Eye is missing.

The Void changed to make room for Simon. The scenes are mirroring each other.

This may be another stretch, but I've always wondered what the hell that big ol' orange light at the top of the tree is... then I kept watching the storyboard. Check this out:

He falls into the Eel's mouth, symbolic of death, and he bursts into literal orange flames. We watch as Simon's soul becomes that burning thing. I've repeatedly orange-coded Simon in the past; it's the literal color of his soul. See here and here, and also here for related art.

Perhaps the "chosen dead" of the Eye become landmarks encased in what the Eye "sees" in them. I think Simon's soul is burning orange at the top of that blood tree, and I think the "Light" was the previous guy that this exact thing happened to. I mean, it's just uncanny...

This has happened before. This is a human soul. It wasn't meant for us to see. Of course the kind of energy emitting from the anomaly is enough to destroy anything it touches, it's pure light. It's us.

Also, an addendum observation...