I think attaching the motor directly to the transfer box and placing it where the gearbox is would free up a lot of space in the engine bay for batteries. Although you'd need to do all the calculations on ratios, both transfer box and diff to see what rpm vs road speed gives you. This
page I've just Googled might help.
If I remember rightly the ECC guys were going both ways, one Defender was having the motor attached to the gearbox the other was going to be direct drive. I'm not sure why they're trying both routes, maybe to see which works best, more than that you'd need to ask them
. My thinking is that if you're planning on going serious off roading or towing you should keep the gearbox, if it's simply going to be on road then direct drive or through the transfer box could be a viable option, as long as all the ratios are in your favour.