Snap uses flatbuffers for nuanmb. It's unclear if the data matches up with any existing ssbh anim version.
ssbucarlos/smash-ultimate-blender#253 (comment)
https://github.com/rh-hideout/rhh-docs/blob/main/NX/flatbuffers/SNAP/nuanmb.fbs
It looks like matinstb is likely also implemented in flatbuffers due to the presence of vtables, array offsets in decreasing order, etc.
I'm not against adding support to ssbh_lib if someone wants to work on it. Using the flatbuffers crate and compiling from a schema should give a much cleaner implementation. I don't want to require installing the flatbuffers compiler for building the crate, so the generated files will need to be checked into source control.