In your Mintest/doc/ folder you will find this file:
mapformat.txt file (at github) that explains how maps are stored in an sqlite database format.
But I guess the difficulty is not really to read the geometry of the world such as there is a node here or there, the problem is rather the non monolithic structure of Minetest. In Minecraft we have a fixed number of node kinds and these are mapped to a single file that includes all textures. You may define a different texture file but it is always this one file and this fixed number of nodes.
Minetest does not use this approach. In fact its very philosophy is to be open to as much content adding by mods as possible. The downside of this is there is no central list of all possible nodes and there may very well never be. The number of node-types Minetest can register on startup has been raised some months ago and servers such as VanessaE's Creative or Landrush may be well beyond 7000 registered node-types by now if I remember correctly.
If you look at the mods listed for the
public servers you may note that almost every one of them uses a different set of mods. In practice this means you even cannot just swap the worlds between servers, the maps would have lots of unknown nodes. That is why some servers that offer downloads of their maps also offer their mod collections they use as Minetest-games or Mod-Pack or at least make an extensive list of the mods they use. Not to forget some servers use mods unique to their server and do not offer them for download on public forums.
VanessaE maintains a pretty long list of
colorsassigned to different node-types for use with the mapper. It may well be the best external list there is of node-types at the moment.
An export program would have to list all the node-types it finds in a Minetest map and then search your Minetest installation for all the textures provided by the used mods, modpacks and texturepacks.
To be honest, I am not really sure how Jordach did it but I don't think he actually opened a Minetest world with Mineblend. He must have used some detour to get there.