I just tested by copying an encrypted sparsebundle I had to iCloud Drive. I could mount it, make changes, and the changes upload when I unmount it. I could then open it on my other Mac, make changes, etc... Seems like a convenient way to keep sensitive data in iCloud, though it's only accessible on Macs because iOS cannot open sparsebundles. I'm just wondering if anyone has been doing this for a while, and if there are any reliability concerns. I was surprised at how well it seems to work; it even seems smart enough to wait until I've unmounted it before uploading changes to the cloud!