This "texture not showing up" problem is tickling the back of my brain. Like I've run into it before making games with DarkGDK. Completely different development environment, but maybe the solution is similar.
I'll ponder it. Maybe I'll figure it out.
lol I should have known better. I tried in Max and Maya, making a simple cube textured with a simple image file. Then I tried using the Nexus Asset Import feature. It said it successfully imported the asset and then opened up a new screen with 3d Preview, Material Editor, Animation Manager (grayed out), and Model Manager.
Then I tried the 3d preview button. I got a bright pink untextured cube on a black background. (This is when I exported the fbx from Max. My exported .fbx from Maya just crashed Nexus.)
So my cube was showing up, but not its texture. Which was odd because I made sure I embedded the textures when I exported the .fbx.
Then I noticed that when I imported the fbx in Nexus, it created a folder with the texture in it! It extracted the texture for me, automatically.
So I tried the Material Editor button.
And this is where I got stuck. No matter what I did, my "Material Preview" was always just a white circle (correction: sometimes it was a black circle). I Added Material, I selected one of the several Shaders which allowed a file name selection, and selected the texture file. But I could never get anything to successfully appear in the Preview.
I fiddled with some of the numbers, changing the AlphaMode or the shader options, but nothing worked.