What are you trying to fix that isn't already possible in either games besides making bus bodies (in Automation )? If it's that "you can't just 'make anything,'" how so? Not trying to discourage you. But BeamNG and Automation have been in continuous development for over 10 years and they have strong modding communities. What are you offering that everyone else isn't? It's already pretty easy to make cars for BeamNG through Automation or modding. It especially becomes cake easy if you have low standards, too XD
You can already do that through modding. Those irl car meshlaps are imported models. Automation already does this, too, only Automation additionally generates a custom jbeam for its models
