This would be a great addition, however I feel that there would be too much work involved with physics engines to accurately portrait a visual cone in the simulated world. Based off of real-world, real-time weather and barometric data, not to mention that by doing so, it would probably dramatically increase the RTM-cost to be able to still turn a profit, it seems like a long shot that this simple visual amenity will get implemented.
What you are referring to is a vapor cone. A vapor cone, also known as shock collar or shock egg, is a visible cloud of condensed water that can sometimes form around an object moving at high speed through moist air, for example, an aircraft flying at transonic speeds at low altitude. When the localized air pressure around the object drops, so does the air temperature. The vapor condenses around an area of low pressure, which can be a sign of an aircraft about to go supersonic, however, the vapor in of itself is not a definite characteristic of supersonic travel.