I rode the TAT on my 8GS camping the whole way, my Nancy rode portions of it on her 650GS. It can be ridden on just about any bike IMO with the right rider, or driven in a mini van for the most part, at least when it's dry.
Nevada and Oregon were in good shape when I ran just those sections again last year, the "hardest" part, taking weather related things out of it, is in Utah.
If you go to my Smugmug, linked from my site there's lots of photos of the TAT so you can decide for yourself. The GS is perfectly suited for the TAT for many riders IMO. You'll need to have a 200 mile range in Oregon for one section, longest between gas in NV is around 150 miles, or less.
Of course roads can and will change, but still you should be fine. Have fun!
Lots of roads that look like this or this.