Maybe this is interesting to you. If not, then sorry to bother this topic. I've written a Minetest Schematic editor, which can generate blueprint images and previews from .mts files with a single keypress.
How to use:
1. install MTSEdit
(available for Linux, Windows and MacOSX)
2. start Minetest and enable MTSEdit Minetest mod (no dependencies, works with all games)
3. select an area in the world, then in the chat window type "/mtsedit save something"
4. open "(world folder)/schems/something.mts" with the MTSEdit application
5. to save preview png, press P
6. to export blueprint png, press E
It can also import and convert many formats (Tiled, Goxel, Magicavoxel, Qubicle etc.) into .mts files, so that you can load your schematic directly into the Minetest game. No need to copy your blueprints in external tools into the world using creative mode any more! MTSEdit does that for you with a single click! :-) (A simple to use, dependency-free Minetest mod is provided to load .mts files into the world)