In December, I visited MicroTek Finishing in Cincinnati, Ohio. MicroTek's proprietary process takes rough parts (often produced by DMLS and EBM) and gives them selectively smooth surfaces; the results are absolutely stunning.
MicroTek is very careful to make clear that their process is *not* polishing, claiming it's more like micro-machining. They're also able to control surface features in highly precise ways, leaving exactly the magnitude and frequency roughness desired. It's a fascinating idea, and one that they're able to charge a pretty penny for.
I've been scheming on using MicroTek on my DMLS seatmast topper; I'll be sure to report back if/when it happens.