It's not just a theory, it's canon.
The Serpent's Spine expansion focuses on the area you mentioned north-westish of Highpass that flows into the Desert of Ro.
Some of the Prophecy of Ro zones take place in this location as well (Takish-Hiz)
See:
[You must be logged in to view images. Log in or Register.]
[You must be logged in to view images. Log in or Register.]
[You must be logged in to view images. Log in or Register.]