There are a couple of aspects of the MGS games that have already been discovered - this leak will help expand a lot of details

We know from reverse engineering efforts, and accounts by developers on the PC port, that all of the mainline MGS games used a proprietary scripting system called GCX. This was effectively a Konami fork of TCL - see eg https://github.com/Jayveer/Gcx

Konami built a custom lighting format for at least MGS3 called LA2, and a proprietary audio format called SDT. So far these haven't been reverse engineered - the leak will definitely open up progress there.