You're right Jahnocli. Animatable Layer positions would be a feature for the next update.
Anyway, with current version you can make your layer animation using the "Sort layers by Depth" option.
To do that over root layers you must set on that option at Project Settings. On the other hand, to do that for child layers inside a Group or Bone Layer you should go to Layer Settings dialog and in the Depth Sort tab, check on the "Sort Layers by Depth" option.
Now you can modify the "Z" position of the layer during timeline and they would go back and front according to their relative Z values.
Extract from the built in help:
Depth Sort
This tab is only available for group and bone layers. Depth Sort has two controls that can be used with Moho's 3D features. The "Sort layers by depth" checkbox allows sub-layers to move in front of and behind each other during an animation. Normally, layers are drawn in the order they appear in the Layers panel. However, with this option turned on, layers are displayed according to how far they are from the camera. See the Tutorials section for an example of using this feature. Typically, layers are sorted by their depth from the camera, but if you're trying to create a 3D object using multiple Moho layers (like a cube or pyramid), you may want to turn on "Sort by true distance". This tells Moho to sort layers by the distance from the camera to the layers' origins, rather than by depth. Usually this option will be left un-checked.
http://www.lostmarble.com/moho/manual/layerwnd.html
Please read the built in help and do the tutorials. They are truly worth.
-G