I might just have to do that -- I got the oversize Mugen battery (with extended back cover) during the first iteration, where the camera etc. didn't work. Since they sent us all two of the new covers after they fixed the issues, I've got a spare to mod on.

Of course, the other thing that comes to mind is USB host -- if one routes the USB contacts out to the back, there should be just enough room in the Mugen case for a simultaneous charging and USB setup, with power from either the touchstone, or through the N900's USB port with an obsolete USB charger (the ones with no connection on D+/D-). Might even squeeze in a USB hub, and multiple mini connectors. I wonder what current the touchstone delivers...