First not a feature, but a bug fix:
Currently, there's no way to add input to the brake of the wheel, it only be applied by pressing the brake, and can not control by FT input.

1.Ball joint
because the ball joint

2.A drive train system
Drag and drop drive train, that has spinning animation, and we can connect one end on transmission, one end to diff (and have settings on trans and diff), and finally to a wheel or a block (for making engine prop using engine power).

3.A holo rim for the wheel with physical tire model
holo in the middle so we can make our own spoke
and we can customize how's the rim size, how tall the sidewall, compound, tire pressure, and maybe the curvature of the tire.
Because the deformation of the tire and change in contact pach is also an important part of suspension

4.engine mapping
It will be a nice opportunity to teach everyone how ICB works
Although I don't expect the level of detail like in automation.
Currently in SP there's some kind of spin prevent mechanism built into the ingame engine, so you introduce enough slip (turning), the engine will automatically cut power. So maybe have option to an/disable that option

5.fixing the soft connection or at least have the option of having stronger soft connection without haveing to add weight