Very nice project, due to previous bugs with GLB shoebox I was looking for possibility to use it in next project, but main issue was that for sound/music it needed to save files on device and was opening them in standard way, so it makes loading times longer when there are many media files :/ (i was afraid specially about Android) And im also not sure how loading from custom shoebox and using Mem2Sprite would compare in terms of speed to normal shoebox. But nevertheless I looked even deeper, in SDL docs you can find function that creates sound/music objects from memory (like Mem2Sprite), but that isn't well documented if I remember correctly so that would be more tricky to do it in GLB. Beside all this it was very promising, and could be even better if additional files encryption could be used apart compressing them as PNG, some kind of password system or byte checks when uncompressing.
Thing about compression, there is minimal zlib.dll version that contains only basic functions for dictionary base compression, curious how this would compare to 'compress as PNG' method. Years ago I made some kind of LZ77/dictionary encoder in FreeBasic, wasn't so good as zlib but still it was only pure Basic code, maybe time to rewrite it in GLB just for fun.
But now with this
load data from memory hack you can rework your shoebox to use this trick and that would be awesome, another possible way of protecting/packing files, I would like to see direct comparison to standard shoebox in some game project.
I also don't have AndroidStudio installed currently

so can't test it that way..