Quoted from Pinchroma:
Powder coating ramps is a TERRIBLE idea. Habittrails are ok as they have a pre-determined path they take so ball tracks aren't an issue. In a ramp you don't want a groove to be created. The powder isn't thick but repeated pathing from the ball can certainly create a valley and that isn't something you want on a ramp.
Have you done it? I have on The Shadow. No grooves on black powder coated ramps after like 10 years. Seems like speculation of people who haven't done it, based on my first-hand experience with actually doing it. Especially when we're talking non-routed pins for the most part.