I think Urithiru is "The Tower" in the Shattered Plains. I don't know how it got there because they DID say they REQUESTED it be built in the West. Shinovar is an extremely good viewpoint. However, there IS a city in the Tower in the Shattered Plains and here are the reasons I think it is Urithiru.
The Tower is a city. It might not be Urithiru, but here is why I think it is.
The Shattered Plains are shattered for a reason. Most places (theory places) think it has something to do with a big event in the cosmere. My theory is that Urithiru was in the sky and fell when Honor died (when the Almighty was overpowered by Odium). You would think it would fall directly down (and therefore land in Shinovar, or somewhere in the west), but perhaps not. Perhaps it was never really in the West and they just WANTED it to be there.
This could also make sense why it seems the voidbringers seem to cluster there. If the voidbringers infiltrated and brought down Urithiru, then that would be their origin, or center of focus. We know (or think we know) the voidbringers are the Parshendi/Parshmen/Chasm Fiends (which all seem to be carapaced animals that can somehow mutate into different forms).
Regardless, there IS a city in the Shattered Plains (it is the Tower).
PS - Why is there so much crem/dust in the air anyway? It makes it seem like either this dust is being carried for MILES (in the air, high - which with the power of a highstorm is possible) OR there is potentially something above them dropping dirt.