It's a very cool idea, but I don't think it will catch on.
Like many have said, there is too much room for error. It's easily possible to short-out cells, but I think (hope) most people would catch that before it caused any damage. My biggest worry looks like this:
/+=====-____(-)
\-=====+\
/+=====-/
\+=====-____(+)
where one cell (in a supposed 4s pack) is reversed in polarity. If you manually set the charger to 4s, the charger will detect the error. If the charger auto-detects (like hyperion does), it will see a 2s pack. If you aren't paying attention and charge anyways that WILL cause a problem. Of course any problem you can forsee with this pack system can be prevented by using caution. However, even I have seen sparks because I was in a rush.
Edit: It may have been implied, but your truck will not run very well, either, if you hook-up a pack in this manner.
