So it seems that BFG is moddable after all!

Check this out:

https://imgur.com/a/byaex

For windows:
download
https://steamcommunity.com/linkfilter/?url=https://github.com/RobertBeckebans/RBDOOM-3-BFG/releases/download/v1.0.2-ATI-hotfix1/RBDOOM-3-BFG-1.0.2-ATI-hotfix1-win32-20140517-git-952907f.7z

then extract it to (steams default location)
C:\Program Files (x86)\Steam\SteamApps\common\Doom 3 BFG Edition\

Download the Hires texture pack from here

http://www.moddb.com/mods/perfected-doom-3-version-500/addons/perfected-doom-3-texture-pack-v20

extract the .zip, then extract the .pk4 into
C:\Program Files (x86)\Steam\SteamApps\common\Doom 3 BFG Edition\base\

run the game with the RBDoom3BFG.exe that you extracted to
C:\Program Files (x86)\Steam\SteamApps\common\Doom 3 BFG Edition\