I agree that it´s not a high priority feature, but more of a finishing touch. However, I do feel like details like that, when they come up, add a lot of flavour to a game. It´s one of those small, but logical things that makes a game world feel like it works according to certain rules that are consistent. A game like Dominions 4 has tons of these and it is part of what makes it special – though I´m aware that adding units is much easier in that game because of their much more limited capacity to act in battle, and the relative simplicty of their designs.
The main issue is how much effort it would take relative to what you get out of it, which is tricky to estimate since I don´t know how Psen made the current Wìedergangers or how difficult it was to program them. If Psen essentially takes the base human model and retouches it, then making more is a fairly efficient process. However, making it from scratch means an amount of effort similar to making a totally new unit model. You can skip part of the design phase due to similarities, but that´s still a lot of work.
If it´s relatively easy to introduce, then you get more diverse encounters and added flavour for little effort. If it takes a lot of effort, then it should be something kept for last or not be implemented, rather than spend time on it better spent on other features.