Well I've had people giving me artwork, music and documents for websites and art and music for my apps. I've had people give me confidential documents that they don't trust, or aren't allowed due to company policy, to upload to any cloud services.
Yes these are certainly legitimate use cases, although I'm not sure how the iPad "Pro" fits into these scenarios. You mentioned apps... So I assume you mean mobile app development? Hmmm... XCode for the iPad Pro? I like the "Pro", but I remain skeptical about the current iOS app selection.
Regarding trusted cloud services, my company has actually worked out some kind of deal with Box to host a "trusted" cloud storage solution.
I've had video clips for my apps that other people have worked on. Lots of photos and video clips from family, we recently had a photo shoot and they were delivered on a single flash drive. That was about 3 Gig of photos, easily moved across.
Then of course, as I mentioned before, there's the recreational use. Sharing a single movie to everyone at the same time when you're on a long car journey, or waiting for hours in an airport.
There's lots of uses for them. Like you I do use cloud services, but they aren't always accessible and certainly nowhere near as good for loading up a portable HDD with films and all sorts for when you're away from home. Not everyone will see a need for one, I always got by with cloud services before, but now that I'm used to the flexibility and convenience of one of these devices I could not do without one.
Interesting. I'm trying to view your use cases in the lens of Apple's "walled garden" approach. It would require everyone using an iOS device and buying everything from the iTunes Store (for sharing films to watch).
If everyone has an iOS / OSX device, AirDrop works reasonably well to share movies (and I guess shared photo streams etc.), although for a photo shoot (I assume commercial) it feels like the workflow would too complex currently within Apple's lineup.
Yes I think I can see how a wireless + thumbdrive storage solution can come in handy. It makes me curious... How would Apple "solve" this "problem"?