The mapzen tiles osm boundaries layer only seems to include lines between countries, not the outline of the country itself, this implies the line mayu not be a closed polygon. You won't get the line running along the coast and Australia doesn't have any boundary data.
Get border data from https://mapzen.com/data/borders/
Printing out a feature (e.g. in a filter), will only print the attributes key.
This issue is relevant to loading topojson sources. https://github.com/mbostock/topojson/issues/242 you need to bake in an antemeridian cut.
The final approach involves loading the map, loading another source that contains polygons for countries; then processing the data for the countries and calculating colors, then updating the scene config to use the new color scheme.