General feedback is per expansion, but usually you can post comments about bugs/issues/ideas not directly related to expansion-specific changes there as well:
Your suggestion probably has the best fit for Player Features and Ideas subforum:
Propulsion mods in the game are not among the types of module that are rendered on a ship (like guns are, for example), thus there are less options to add visual effects to them. When you turn on AB or MWD your thrusters exhaust visual effect increases, so that is taken care of. Other than that, what kind of a visual effect did you have in mind?