First ,I'm not saying I want this, so you're addressing the wrong crowd.
Second, there's little difference between a thumb drive and a hard drive as far as the device you are connecting it to is concerned, so if they allow one, the other will work.
I agree that simplicity is good, but it is workflows that need to be simple, not devices. If making the device more complex so that it's simpler to do my job (printing out something by plugging in a printer, scanning something by plugging in a scanner, docking my iphone to my ipad to share information, etc.) then I'm all for it. Wireless printing == fail, because most printers aren't wireless, and if the workaround is software on a host computer, most computers won't have that software, for example.
Transferring files across my work firewall doesn't work, so I use a usb thumbdrive to take files back and forth to my MBP. Wireless is not a solution that works for that. Etc.
Second, there's little difference between a thumb drive and a hard drive as far as the device you are connecting it to is concerned, so if they allow one, the other will work.
I agree that simplicity is good, but it is workflows that need to be simple, not devices. If making the device more complex so that it's simpler to do my job (printing out something by plugging in a printer, scanning something by plugging in a scanner, docking my iphone to my ipad to share information, etc.) then I'm all for it. Wireless printing == fail, because most printers aren't wireless, and if the workaround is software on a host computer, most computers won't have that software, for example.
Transferring files across my work firewall doesn't work, so I use a usb thumbdrive to take files back and forth to my MBP. Wireless is not a solution that works for that. Etc.
Well, there's an adapter for SD and USB (and as I recall the iPad has a higher voltage available through it to support more external devices), there's no reason it technically couldn't work, but I don't know that Apple wants to enable all that and the accompanying support headaches, honestly. A hard drive attached to the iPad, really? Sorry, but I doubt that's something Apple has in mind for the iPad. Once again I have to say you're not anywhere near the target audience they have in mind for this device. As far as Apple is concerned, that's what their desktops and laptops are for.
Printing I can see a need for, at least wireless printing. I do think you will see that and last week there was some report about APIs for that found in the iPhone OS. That'd be great to let's say sign in to your airline on Safari and quickly print out a boarding pass. For more critical printing tasks, again, do it on the desktop machine.
What I'm trying to say it don't expect the iPad to do everything, to replace a desktop or even a laptop, at least for a power user. It won't and Apple doesn't want it to. Simplicity is the key word when you talk about the iPad. Anything that makes it more complex or ungainly has a high probability of being shot down, and that includes not only hardware but software such as full multitasking.