A fun fact, Comets are actually fully modelled by Stellar forge. They are known to exist in Sol (Halley's comet) and Pareco (It's what all the stations are """orbiting"""). I wasnt able to find records of one being spotted in deep space, likely due to their tiny radius... but they do exist! They just have no graphics as of right now, making them near impossible to find.
For the in-space visuals, you can reuse the supercruise plume that many ships already have. Attach it to the comet and have it point away from the object the comet is orbiting. For the comet object itself, you can use an icy or rocky asteroid model.
Higher dev cost would be actually modeling the ion tail and not just the dust tail, as well as a special/custom asteroid model, but would also look wonderful.
For the in-space visuals, you can reuse the supercruise plume that many ships already have. Attach it to the comet and have it point away from the object the comet is orbiting. For the comet object itself, you can use an icy or rocky asteroid model.
Higher dev cost would be actually modeling the ion tail and not just the dust tail, as well as a special/custom asteroid model, but would also look wonderful.