It seems likely to me that cars (in whatever form and application they ultimately take) are probably somewhere in the development process, but require a lot more work to develop and integrate on existing maps (which may need completely reworked) than making a new animation and object would be. It seems like they've tinkered with the possibility of cars or reworking of roads and maps for a while now, and that it's been a challenge for them to figure out. I don't think they can really tell us if they can or won't add cars, since they may not know themselves yet, or it's coming along and in the years-long development process.
