It's great, but we're very far from the os-agnostic seemless integrated files sharing.

You see, we have protocols like HTTP and the web relies on it, everyone agrees this is how the web works and all OSes have one or several browser able to access it. Something similar works with emails. Yet, we don't have anything to share files between computers, imagine something like bittorrent directly integrated to all OSes, letting you right click > send to.