In theory you can already import from any cloud provider that is set up on your iPad. Just tap on “Locations” after you selected iCloud from the import screen.
In iOS 11 though it will be even simpler as the Files app will congregate all your files into one place.
One problem though that we haven’t been able to figure out yet is that Google Drive doesn’t recognize the file types so for now you can’t import using that service. We hope we’re gonna be able to fix that soon.