The biggest fear would be that any NWN:EE would be updated with modern 3d graphical features. i'm not sure anyone would want to risk investing in a NWN:EE while changing so little graphically so it does not break any custom content. I can see the benefit from adding multi core support, steam cloud integreation, gamespy replacement and the like. but i fear it would be bundled with bump mapping and physically based rendering.
I also used worry that an enhanced edition might potentially cause problems for existing custom content but, based on what I know now, I can practically guarantee it would be impossible for a situation like that to come to pass. So, the scenario of an EE "breaking" existing custom content isn't even an issue.
The parts of the game that a (basic) graphics engine update would touch would have very little to do with how custom content is made but a lot to do with how it's expressed, visually. So, for instance, in a hypothetical "typical" NWN:EE, it's very likely that all the creature and tile models would be exactly the same as they are in the NWN:Diamond that people buy off GOG.com nowdays. There might be _additional_ files (like bump maps or additional texture information) that would cause enhanced functionality to "kick in", but it would definitely not be a big change across the board.
NWN already has functions inside of it to do bump mapping and rudimentary physically based rendering but, for the most part, these commands appear to have either been disabled in the renderer or do something but do it inefficiently. As far as rudimentary PBR goes, some examples are the specular and shininess model settings and TXI commands like specularcolor, isspecularbumpmap and isdiffusebumpmap. Even if these things were enabled, they're still pretty primitive. We're talking specular stuff on a per-mesh level as opposed to having a specular map, but it's still stuff that's already in NWN.
