If you're talking about the /dev/fsa stuff, that's because all that is on the Wii U itself. You hit the nail on the head when you said the calls were read/write etc: all the encryption is handled by the backend and not by homebrew; we just get to read and write the already-decrypted and interpreted content. It's literally "find this file"; no "decrypt the device, now loop through the filesystem table, now off I go to interpret that..."
Because of this, there's not much understanding of what actually happens behind the scenes, and certainly not much on the filesystem (ISFS/ESFS) itself. Somebody would have to reverse-engineer the IOSU's firmware to figure out what it actually does to find the files we ask for. While not impossible, ARM assembly is no PowerPC and reading that stuff is headache-inducing. Good luck convincing anyone, especially with libfat on the way (removing the need for homebrew to use ISFS/ESFS at all).
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NormalCatelol:
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The Real Jdbye:
