We need blinkers [which are easy with cyclic animations; according to Teneksi (I will test this out later on)], Nitrous?, Animated Speedometers and actual engine sounds.
Well, it's fairly easy to do blinkers in a way that would be possible, but may result in single frames of sketchiness (you know, when two parts of a model overlap exactly). I know of a way to make those more rare, but they may still have a low chance of appearing. Using hideNode and unHideNode would be much more reliable, and, since it's not nearly as complex as emergency lights, it doesn't pose as much of a problem of becoming a visual lag meter. However, custom headlights and taillights which are changed with CVS would be problematic, unless it would be possible to parent some function from support_garage and let the blinker script know which version of the signal needs to be used. Or, I could get in contact with Barnabas and hopefully he could explain (for the third time!! apparently I need to learn to take notes or something) how to make an animation which can make a part disappear rather than scale it.
Nitrous might work by adding velocity to the vehicle in the direction it's pointing. This is not the same as adding more torque to the wheels, but this doesn't seem to be an option. If the vehicle's mass was high, velocity could be added repeatedly until it's at max speed (a max speed which would be lower than 200 or 300 BPS)
Animated speedometers would be possible but would require a lot of animations. Possibly, single-frame animations. Of course, either this would need a great number of nodes, or it would take up an animation slot, which are very valuable to those who seek working doors.
I have made a speedcheck-based script which uses a combination of speed and acceleration to play engine sounds which rise or fall depending on whether the vehicle's speed is increasing, decreasing, or constant. It still sounds odd at times, but it's much more immersive than the typical engine sounds we've encountered.
I would say that Vehicle_CrownVic2016 (still in progress) is a progenitor for what you might call the third generation. The video which will accompany its eventual release will explain just how extensive the changes are. I've made many of its changes in ways that should make it relatively easy to apply them to future vehicles, and I'd be glad to explain how to use them (although please wait until I've actually finished the car; some of the scripts have improved dramatically despite working in the same way)