That's pretty interesting..hmm..Most of this I'm pretty sure we already knew, not all though so it's an amazing find. And yes, that's most definitely the start of a level editor from what I was reading. Either that or it's just going to be a map viewer. If I read some if it correctly, barely thanks to google translate, then he's also having some issues with the map layout and the enemies as well.
The X3_AD001 folder..Not entirely sure what it does but I put a Rock Man X3 rom into it and it output a file of 28 megs that was a .asm file. It looks like it broke down a crap ton of the game into ASM but I'm not entirely sure.
If he keeps it up and releases the source codes as he goes, this could be a great start to a universal MMX3 Editor for both the JP and ENG versions.
Edit: It seems Zero has some unused frames.
You can check in game if you want. You can clearly see where they should be used but they're not used. Sort of strange really as it helps smooth out the transition.
Here's what his dual buster attack looks like with and without the unused frames.