I don't know exactly, but, I think the Minecraft storage format is pretty straightforward - a 3D bitmap, effectively. There were loads of 3rd party applications interfacing with the application years ago, ranging from external design applications, a live Kinect-into-minecraft thing, etcetera; I have no doubts that the Minecraft data format will be very archivable and that an open source viewer will be relatively easy to make. See also: https://minecraft.gamepedia.com/Programs_and_editors/Mapping
NBT and the newer compressed mapformat Anvil (developed from MCChunks mod if memory serves correctly) is not that straightforward to parse and lots of tools easily corrupt Minecraft worlds. In addition to that, you can then compress again using gzip or zlib (with little indication of which you picked other than "try and see which one crashes"), in some cases certain NBT files cannot be compressed in others only one compression is allowed.
The data is also big endian, unlike most computers use internally (unless you use Pocket version then it's little endian, and again, isn't specified which to use).
The current anvil format isn't a simple 3d bitmap either, it uses various method to compress out empty space from the 3d bitmap and leaves out any chunks that weren't changed at all since generated.
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