I did not want to parallel modules, and then wire them in series, due to the potential of one of the cells shorting.
I am sure Nissan has already did the math and has figured out that the 2s2p module can handle the energy from one cell shorting into the other cell.
I doubt it could handle the energy of 3 or 5 cells shorted into one cell.
The other advantage is redundancy, if one of the four 150V packs has a problem, the power controller will disconnect it from the main DC bus, and I can still make it home on the other three.
On my lead acid pack I had a battery connector fail (cracked), but I was still able to make it back home on the other working half of the battery pack. 24 12V batteries, two parallel strings of 12 in series.
Same with the power train, I have smoked a motor controller and still made it back home on the other one. And have broke a belt a couple of times, but I can always make it back home to make repairs. ;D