ThomThom wrote in "forum.sketchup.com":"......but the API doesn't provide any control over them.
@tyler_miller - got the history behind this oddball of an entity?"
Is there any news yet?
Some related questions that may expand the use of these 3D Polylines:
Can edges be converted into (i.e replaced by) components containing one single edge per component. One "single edge" component with scaled versions replacing all the edges in a selection.
Next step would be to replace this component (and all its scaled instances by a "single segment" 3D Polyline component, scaled likewise per edge component. This component with standard length, say 1m is already an "In Model" component.
This would allow replacing a wireframe by a 3D Polyline version that doesn't interfere with the inferencing engine and serves as a visual reference.
Some examples:
-1) visual marks in a model, easy to spot (whether accompanied by a guide point or not) each with its own color, even with edges colored all the same.
-2) visual referens of axes in a different color (for color blind people)
-3) symbols that are visible in the model but don't interfere with what you are modeling (no snap to)
(Mike Lucey at SketchUcation once mentioned working on symbols, using edges and faces. But the cursor keeps snapping to real geometry). example: 2D vegetation.
-4) accurately dimensioned (scalable) visible circle or curve, not interfering the inferencing engine.
-5) though limited, two styled in the model, say straight 3D polylines plus a sketchy style.
-6) maybe some other options.
If replacing edges for "single segmented" 3D Polylines through plugins as mentioned above isn't possible, -1) trough -5) is still possible but very laborious, some more than others.
edited:
-6) completely transparent hatches opposed to faces textured with hatches.
-7) (3D)text, visible though not in the way when modeling.