I understand this is an old topic but I was looking for anyone who was attempting 7 string support in Rocksmith, and this looked fairly promising even if just displaying a custom guitar headstock. I have a lot of experience in the Bethesda games modding space which uses the same engine, and file types for models and would very happily offer any assistance needed. I have 3ds Max 2013 and tools to convert to .nif file formats. I am also a professional 3D artist and would be able to create assets for custom guitar models.
Sadly having a custom guitar model with extended range doesn't actually generate extended range notes on the screen, or allow EOF to chart them, do any of you have ideas in the works for getting around this?