I got a look at one yesterday. While the Pi-related features may not be worth it to you...
I have not seen one, except what WD put into their news releases last week.
I am not at all sure there are any Pi-related features, besides Pie day and a discount.
If, for example, the power management in the drive has been altered, so that during both startup and normal operation the drive does not exceed the RPi power allowance per USB port, then the complex cable is not needed.
I have not seen a picture of a case, but I am looking forward to hearing more about it,
(or seeing a photo)
WD has a proven record for making reliable drives (IMO), which I use and like, both in personal use and work. I have used WD "Blue" (2.5") "Black"(2.5 and 3.5"), and "Red" (3.5") drives for years. unfortunately, Western Digital does not excel in marketing and information distribution (again, IMO).
If the cable is needed, because the drive EXCEEDS the power allowance of even the newest Pi, then you may as well use a WD Passport (another product I like) for $59/1TB retail, and a USB hub, or a Y-cable, or any one of the other solutions people are using now.
As for USB 3, the drives inside the WD Passport have had this for a long time.
RPS (reduced power spinup), and a list of WD drives with their typical and maximum startup current listed, would surely be of interest to RPi owners, and increase interest in Western Digital 2.5" drives in this community, and
help sell more WD drives, even without a Pie-day gimmick, and without resorting to RC cars to attract attention (again, IMO...
See example article:
http://archive.techarp.com/showarticlee ... 665&pgno=3