Honestly i'd love to see a mod, or update that makes a jake brake for the T-Series. It seems fairly simple and straight forward to make, and even if it was just a sound it would add a whole new feel of realness to the semi'ss in the game!
https://www.beamng.com/threads/t-series-experience.71893/#post-1190419 Due to a current lack of time to mod it's going to take a while to polish this up and share but eventually it will be finished within a few months.
i also would like to see realistic air brakes. https://en.wikipedia.org/wiki/Air_brake_(road_vehicle)
yeah would be nice if there was air supply system and possibility to lock brakes because of no air pressure in system.