Uh. Air suspension LOL Being able to air out, and then increase ride height again with the push of a button would fill that void in my life with my car well in this game.
How about self-leveling suspension? I've been wondering if someone could code a simulation of Citroen's hydropneumatic suspension on, say, the ETK I-series. As for air suspension, there are many mods that accomplish just that, take a look at the repository.
I had also thought of adaptive suspension etc. It'd be pretty neat to see. I'll check out the air suspension mods but I generally don't use mods if they're not up to par with what's already released ingame quality wise.
Air suspension exists in the game using mods, adaptive suspension also exists in the Vivace/Tograc and the ETK 800/K series.
Upper trims of the Grand Marshal and Roamer actually would be realistic with self leveling air suspensions. That would be pretty cool.