this is one of those suggestions that I would have coded myself, however your mod is of the complexity, right now, it would be better for someone who actually understands how you have structured your mod. And I am aware of the rather simple explanation on your wiki and have read it thrue to the end.

now on to an explaination of this suggestion:
It would be nice to ba able to specify if a building has to be located next to another building/highway/monorail/distance_from the center of the city without having to create a predefined city. and this is not the same as the multibuilding that can already be created but would rather apply to the placement of both buildings and multibuildings.