So, I realized a few things.
First, Wraiths finally looks like the kind of unit you might want to put Ankaur Maro's cavalry upgrade into. The Death Knights would be horrible, as they're high defense, high points, low wounds. This means that an upgrade that eats away at their wounds is terrible. However, Wraiths are low defense, low points, high(er) wounds, so eating away at their wounds is great. And they're a lot faster and more maneuverable than Reanimates, so there's a pretty strong benefit to putting him in there instead of just dumping him into some Reanimates.
Second, I realized that Wraiths do not have a Champion upgrade slot. This made me very sad, given the first realization.
Third, I realized that they have two Unique upgrade cards shown on the image. These images aren't always accurate or final, but if they do have a second unique upgrade, it might add a Champion slot. There's certainly precedent for an upgrade that does nothing but convert to a different upgrade slot (like Fallen Hero) and it would sort-of make sense from a design perspective if they wanted to prevent you from taking Undying Hate and Ankaur Maro in the same unit. Right now, the cheapest you can field in-unit Maro is 55 points, giving him 26 (regenerating) wounds to chew through (or if you're running solo Ardus, 46 points with 18 wounds). If Wraiths do get an upgrade like this, you can run him at 37 points (plus whatever that upgrade costs, but I can't see it being more than 3ish points) with 9 wounds to chew through, or 44 points (plus upgrade cost) with 13 wounds. And all that at much more movement speed to be exactly where he wants to be.
Thoughts?