From the introduction: "On the other end of the spectrum, formats such as HDF5 and BLZ address problems with large data sets and distributed computing, but don’t really address the metadata needs of an interchange format. ASDF aims to exist in the same middle ground that made FITS so successful, by being a hybrid text and binary format: containing human editable metadata for interchange, and raw binary data that is fast to load and use. Unlike FITS, the metadata is highly structured and is designed up-front for extensibility." [0]

Frankly, I feel like making the metadata of a scientific data structure human-editable is something of a mis-feature, or at best a non-feature. I use metadata in HDF5 files as a form of provenance tracking and I'd rather there be some friction to editing it.

[0] https://asdf-standard.readthedocs.io/en/1.0.3/intro.html