You do realize how much instant travel already exists, yes? You can neck to
Dragonhorn
Stormkeep
Rivervale
Grobb
Newport
And from Newport you can instantaneously get to Underhill, Oggok and Sadri Malath. The only place not reachable with out a boat trip is Erudin, and you can just bind there.
I have Rabb in Erudin, and he can get to the mainland with Newport neck and then get to Faydwer with a translocator, to south mainland with the Grobb neck, and to the north with the SK neck. The only place I can't easily access is the east side of the continent because he lacks the Rivervale neck, but with that he could bypass the Badlands.