So I started writing one myself: https://github.com/madmaxoft/MCSchematicToPng
So far I've got the basics working, it exports the PNGs using isometric view of the schematic, using solid colors for the blocks.
Example output (from the Nether gallery on the Gallery server):
So far I've got the basics working, it exports the PNGs using isometric view of the schematic, using solid colors for the blocks.
Example output (from the Nether gallery on the Gallery server):