I’m not clear what the OP means by lighting. There are so many aspects.
If you mean light pools coming from assets such as loco headlights, lamp posts etc. then these already exist in their hundred (probably thousands).
The in game lighting is a different matter. I think it works well, casting a darker (not hard) shadow on the sunless portions of the terrain. In addition this changes according to time of day. Furthermore it will change according to the latitude set in your route with a remarkable level of accuracy.
In the World flyout you can change the lighting dynamics to an unlimited degree. I’ve hardly started on the potential of those controls.
With assets, the shading cast by the in game lighting is dependent upon how well made the models have been made. Most of the better creators (but not all) will build in a shading effect which will match the lighting cast by the sun. You can check this by looking at an object, and changing the time of day dial. You will see the shading move around the object.
Many assets, such as houses and rail carriages, are created with internal lights which automatically illuminate at twilight and turn off at dawn.
Hence my confusion as to what you mean by lighting. What improvements exactly are you looking for?