The basic problem isn't new, and the double-port lead, one just for power, was usual for the earlier portable drives. But now there is more stuff using USB. And some portables don't even have two USB connectors.
I could see an extension cable working to extend either the data or the power input, so you could get power from a car lighter-socket. A simple idea for the show-off market: a laptop briefcase with a built-in 12v input (car electrics compatible, so the input voltage can be higher, but that's a solved problem) with a powered USB Hub that could power the drive, or recharge the computer. I might have an external power-line-only USB connector, but not the data. It starts getting complicated, but having the locked case data-secure would be a selling point.
Using a "proper" hub able to sit between the computer and the drive, and supply the drive from a single power source while handling the data at full speed the computer's port is capable of would beat a 2-to-1 lead powered from two separate devices.
On the other hand, a huge portable drive such as these is maybe a bit too many digital eggs in one basket. It's an option I would be wary of.