So I saw this video of Construct3D's experimental 6-in-1-out hotend that aims to get 200 cu mm^3 per second:

They got the part tested to see how much the actual part deviated from the CAD file, and they were "only 50 microns out in some places". One of the issues that they want to look into solving is the surface texture. 2 commentors I saw suggested "extrusion honing", which puts abrasive paste through a pressurised channel to smoothen the walls.

This suggests that something similar could be done with abrasive filament. I believe glow-in-the-dark is one of the more abrasive filaments commercially available whilst also being relatively affordable.