I had the fortune of talking with a few other folks with the new 4wd prototype. The battery position appears to be an option, simply by where you put the strap down mounts (for saddles or for shorty). It was suggested that one is better on high bite and the other is better on low/medium bite. The other thing that was very clear (and you can also see in the build picture above), is that the steering mechanism is improved, more similar to how the RB6 does it.
The last thing that was mentioned and I thought extremely interesting...was that when they tried the new 4wd for the first time, they simply put the same setup on it as the zx5 setup they'd been running, and immediately thought the car was a lot better, without even trying to dial in the new setup yet.