Sound like reasonable idea.
We should wait for fix of that sound bug with Castellans, and then we should see about soundsets distribution.
Simply I found Castellans very cool unit, they deserve some good soundset, I think that soundset I proposed fits very well, but we should wait to hear current sound set of them, and then discuss.
Anyway, wraiths are units on bottom of priority list, soundset which remains goes to them. That is my opinion.
Sum of all what I said above is that we should wait to hear current soundset of Castellans, after that we will discuss about distribution.