There is already a long thread somewhere about how to do town growth modelling for Experimental - most of these things will be (or already are) dealt with either directly or indirectly. Private car transport is already simulated, as is congestion, but to a very high level of abstraction owing to the computational intensity of doing anything else. The interrelation between industrial and passenger transport is intended to be simulated, and per tile desirability (and not just from transport) is necessary. Travel time determines success rates (these data are already created and stored), which in turn drive local growth. The availability of buildings in any given era will prevent Georgian skyscrapers. Density will require some careful thought but is not too difficult to attempt.
It is a mistake, I think, to think that, because Simutrans focusses primarily on transport, city growth is unimportant: in reality, the growth of towns and cities and the growth of their transport networks are so closely interdependent that one cannot satisfactorily simulate one without simulating the other. A city simulator, do not forget, simulates only one city (and simulates its police, fire brigade, health care, water, sewerage, education, parks and recreation and other such things that are not dealt with in Simutrans), and not the transportational relationship between cities. There is nothing in existence yet to my knowledge that simulates city growth realistically in multiple cities as well as the transport between them (and the relationship between the two).