I'm not sure an Ulgu Orb of Sorcery would actually be the best fit for the Ismuir Road. It's an area ~20-25 miles long that needs to hold an enchantment, that seems like something that could be better served by a bunch of powerstones distributed along its path.
I feel like we should be looking into connecting the road to the trees and through them the waystone network, not that I am sure that is even viable.