Sayd Ûthman said:Would be nice (if possible) to have normalmap and specular shown in the preview screen
Isn't it like that already? You should be able to enable/disable normalmap and specular map when you look at a mesh which uses a material with them. Try disabling the (color) texture map to see more clearly what difference they make.
About the Undo command: you are right, it would be useful, but it is a bit of a mess...