#4 is interesting—but how do you define "devices?"
I have, say, 500GB of music. It doesn't fit on my laptop, so it "lives" on an external HD. Could it sync the laptop with the HD so that I always still have access to a set chunk—say, 10GB—of my most-recently-used music files? This is a capability I've been waiting for something to support ever since I bought the drive.