I still can't find a definitive solution or "don't even try" conclusion, so let's see if one can be generated.

The issue is this. In both High Quality AND Viewport 2.0, even properly mapped transparency renders incorrectly. By incorrectly, look at the attached picture. I have circled and annotated some of the artifacts.

Artifact 1: there's a small sphere on top of the palm tree that these fronds protrude from. You can clearly make out its outline in the image, despite there being fronds in front of it. This only occurs when there's a transparency map applied.

Artifact 2: you'll notice that there's a frond close to the camera, but the frond circled is at the back of the tree with respect to camera. You can still see it. Furthermore, the palm tree trunk is visible through the front frond.

There are many other instances of this artifact throughout the image, but those are the easiest to point out.

I dont think the issue is clipping planes, and I've tested all logical connection configs I know: file.colorOut >> shader.transparency, file.alphaOut >> shader.transparency[R,G,B] (with [alpha is luminince] ON and OFF), inverted colors, etc. Artifacts remain.

Why this is a problem: I want to render with the Viewport 2.0 render as a final output because once everything's built I'm going to need a lot of speed and flexibility during animation and render time due to the project not having concise storyboards.