[HoneyFox]

I took several hours researching the j3d file format, and here is what I've found (see attachment).

It's written in C++ style, although C++ doesn't support declaring array of uncertain length, but... you get what I mean.

PS1: There are still some unknown items, but they seem to be constant during my research over dozens of .j3d files.
PS2: It's still far from having a new exporter. Major challenge is to find a suitable input model format and write a parser for it, especially when dealing with models containing hierarchy.
PS3: Actually I'm not sure if that use_tex and render_order is correct or not, I found no value to store the material index of model, but it doesn't seem to match if we assume it is.