For apps that support it, the new iCloud Drive feature (iOS 8) gives you a feature similar, but not quite the same as general file storage. You can not access it directly from the iPad's system, but apps that support it will let you look at, and even edit, files in other apps (if they are compatible). So you could use an App like GoodReader to open or import files.
Exactly what and how this will work out workflow wise is still unclear. It's early days.
Because the files are in iCloud, they are available on other platforms as well. On the Mac it looks like any other directory. I'm not sure how it works on Windows. You can also look at your iCloud Drive files on the icloud.com site in a desktop browser.
There are two downsides. One, it requires an internet connection for updates. Nothing will get updated between devices and iCloud without an internet connection; and you can't implement it on-device only.
Two, if you use it for more than trivial amounts of data you'll quickly blow through the 5 GB limit of a free iCloud account. At 99 cents a month the 20 GB plan is probably enough for most people. Larger plans are available.
Also, not every iCloud Drive folder appears to show up everywhere. So far that seems to be a matter of whether the file types that are 'supposed' to be stored in the folder are usable by the other device.
Anyway, it's a somewhat more flexible system than the old one; maintaining the security but at the cost of some underlying complexity. When it works it should be a decent, simple way to access your files from multiple devices and apps. When it doesn't you'll probably never figure out why it doesn't.