Just to make it clear, the Power Pack 4000 isn't a "Quick Charge"/TurboPower battery pack.
Will a quick charge 2.0 car charger work on the XPE?
This has been confirmed by Motorola. Using a lower gauge USB cable could possibly impact charging speed and damage the phone, the wire, or the charger itself so they went with a one piece unit to avoid issues. I think it's a smart idea.
I'm not sure I understand the comment in the OP for the need to carry two cables.
Will a quick charge 2.0 car charger work on the XPE?
There are non USB cables used for other portable devices that are two pieces to mitigate potential bend/damage issues at the base of the brick. It will be interesting to see how folk's batteries hold out that use the fast charge all the time (9-10 months). Motorola is being very aggressiveFar more than Samsung with their fast charging.
Cable design seems fine, so probably no harm no foul.
Can we please get over the notion that Quick Charge is going to ruin your battery? I have a Droid Turbo that has only been charged on a Motorola turbo charger since the day it was released, and it stays on the charger all night.(will be a year in Oct) My battery is just fine and still last as long as it did the first week. Motorola and Qualcomm have both directly answered that question on their web sites. They unequivocally state it will not harm your battery. The software and hardware used in quick charge is optimized for the rate a battery can intake a charge.