There is a technical issue with that where the bounding box of the rant does not have all equal edges, and that is a problem for the reasons I have described in this post: http://forum.grangerhub.com/t/tweak-collisions-with-slimes-and-trappers/3574/4 .
For wall walking, it looks the best when all edges of the bounding box is equal in size, and when the bounding box is relatively small. Otherwise either the model would stick out of the bounding box "too much" or the model would look like it is floating away from the surface it is suppose to be attached to.
As a side note, the F server did give wall walk to all of the alien classes. But even with appearances aside, I don't think that all aliens should have this ability, some distinctions in abilities in different classes makes the game play more rich and strategic.