Congratulations on a monumental milestone! HFS+ is a big step.
I still hold out hope for DC6 NDIF image compatibility, but I know it's a tougher problem than most, given that most such files are compressed.
NDIF is a tough egg to crack. The compression is part of the issue, but the lack of documentation is a bigger one as far as I am concerned. There's a lot of "feeling things in the dark" experimentation involved.
Right now, my path is to start further down the timeline of image formats, with UDIF (which is much more documented), and try and see what I need to take
away from it to get to a working NDIF implementation. There is a filiation between the two, so it could be workable.
It's probably a silly way to go about it, but a very strong (and probably foolhardy) goal I've set for myself is that DJ must be built entirely from scratch. There is no external library involved*, no code stolen from anywhere (not even a copy / paste from GitHub) and the resources I use for development have to be historical (no modern blog post explaining how something works can be used). Yes, I'm a paying subscriber and avid consumer of archive.org
I want to build it entirely by hand because I enjoy the journey immensely**.
So, solving the NDIF problem pushes the limits I've imposed myself, but I'm relishing the challenge
* Except for Sparkle, which handles the auto-update mechanism, because that's a problem space that doesn't interest me at all, and the library is very respectful of users and their machines.
** There's a part of my brain that lights up when I work on it, because it harkens back to my childhood. I started programming on a CoCo 2 when I was 9 and, back then, it was mostly me just throwing syntax around to see what would happen (and the fact that BASIC was in English while I was a French native only added to the "magical incantation" approach of it all).
Being able to revisit the magical machines of back then with an adult eye and decrypting how they worked inside using period-authentic documentation is an absolute thrill. it's almost therapeutic