I believe guys will provide some kind of interface for modifications in the future, but I dont expect it to be soon.
It's not that complicated, as you said. A while ago I started writing a wiki-page about GUI modding, so you can track it here. There is a LOT of work, but someday it'll be done
The problem in modification of this game is that Fonline team took closed source approach. Yes - they rely on old fallout files, which will be closed for another 20-50 years, but they, IMO, made a mistake by releasing closed source of their wrapper-engine.So you have 2 choices actually. Get the undat - extract critter.dat and master.dat and try to understand the closed-source file structure and scripting. Another choice is to hack the client itself.I believe guys will provide some kind of interface for modifications in the future, but I dont expect it to be soon.