A novel from Tanus' perspective would be a very philosophical read and full of conflicting emotions!
We already know about Lord Intef's hand in Tanus' father's destruction, so would be interesting to see it from the point of a young and naive Tanus. Also, when Taita tried to convince Tanus to take the throne from Mamose, there must have been a lot going through his mind.
Yeah, I'd read it! But on the downside, isn't Tanus a 'typical' hero? WS would have to spruce it up a little. Prequels are tough to work out.