I am sorry but the answer to all these questions is no. Currently I am not planning to support any osm formats because I have zero knowledge about osm and converting osm xml to json won't help because json the City Viewer requires is generated only by the applications of the Procgen Arcana family. Maybe one day someone will make a converter from osm to this custom json format...
By why do you even need the City Viewer? This is just a minor tool to support the city generator and other generators of mine. Aren't there better applications capable of exporting 3d models?