This should greatly assist builders in achieving better-looking creations, along with variations, without increasing the face count. Normal mapping is a great way for adding the extra detailing without having to add in those extra faces. It will help with saving on prim count, thus increasing server (and probably viewer depending on how complex the mapping) performance, and reducing cost of having to re-upload something to add more detail to the model.
However, even though it is a great add-on to second life. I think it should be set that normal mapping occurs at LOD0 (closest to the object). This way not normal map needlessly added to the query for people to load when not even get close enough to notice the difference from the applied normal mapping. This in turn helps with decreases the reduction of viewer side performance from possible overly complex normal mapping having to be needlessly calculated.
The feature would most likely take some time to implement and make stable sever side (as it has been a few months already). It would probably be along with another major update due to it most likely requiring a remake of the in-world editing sections. I believe that it should have its own tab, and not added to the texture tab. Each section should have its own tab: General, Object, Features, Texture, Normal, Specular, and Content.
Normal Mapping and Specular Mapping needs to be separate from the already existing texture tab. Having them added to the already existing texture tab would make it extremely long and/or abnormally wide when compared to the other tabs. It would also reduce future possibility of expansion for the new features if clumped together. If not done in the beginning of implementation, it would become required when expanding the feature customization. Feature expansions such as the level of strength, and default or planer mapping (of using a design normal or your own).