Is it possible animating the wire frame material Changes to surface material?
I don't know if there is a better way (I don't usually use Blender Internal) but this can be done with material nodes to generate the wireframe using the UV coordinates.
To generate the wireframe we can use the default unwrap (or use UV Unwrap->Reset to reset back to default) and have the material solid if U or V is less than 0.1 or greater than 0.9 (use values closer to 0.0/1.0 for thinner lines).
To get the wireframe to slide across the mesh we can split the coordinates into the respective components and use Math nodes to generate a cutoff, keyframing the value to animate the transition. Note that I've used the X coordinate (split from the vector using the Separate RGB node (RGB translates to XYZ), combined with a fraction of Z so as to make the transition plane not coincide with the sides of the cube (or you get an ugly transition as the whole face jumps between being transparent and not transparent).
Ensure to enable Transparency in the Render Pipeline Options of the material to allow transparent materials.
This produces the following result :
Here's for the crazy ones:
From Haunt's trick bag:
I have two pencils and a huge cube. I animate the cube so one side of it serves as the transition border.
Both pencils have a Boolean Modifier using the Cube. It's just that one pencil keeps what sticks out and the other keeps what's inside the cube.
The boolean modifier has the cool feature that it will use the first material slot for the new faces. Which means for the pencil sticking out, you need to create a transparent material for the first slot and assign the other three slots to the faces.
For the pencil sticking inside the cube, it's irrelevant since it's a wire material. If you need the transition plane completely wire free, you'll probably need two cubes with both booleans set to difference.
Did I mentione that there's yet another way? No?
Well, there's yet another way!
The trick is kind of the same. You have one pencil with the wire material and one with all the rest.
All materials share the same blend texture with cranked up contrast to narrow the transition zone a bit. This texture controls the alpha channel. -1 for the wire, 1 for all the ordinary materials.
The materials need Z-Transparency enabled and alpha at 0.0
And the trick is that the blend texture gets object coordinates. That way, you can animate an empty and decide where the border should be.