Some amazing volunteers have been updating Minecraft Overviewer to work with the new 1.13 file format. I am running a test version now. It estimated sixty hours (!) to render the new map from scratch, but it’s going a bit faster than that.

UPDATE: The rendering is finished (in just under 30 hours) and the new map is installed. As expected, there are blocks that don’t render but overall it looks good. Check it out!