It doesn't matter if the technology exists (which it does) what matters is if the vendors will cooperate (which they won't).

If there was a standardized protocol/system for "cloud syncing" of files it's entirely likely they would all support it. Kind of like how they all support SMB/CIFS now.

It's not a protocol issue.

A universal protocol would only handle the "data in flight". The other issue is "data at rest" which is storage problem.

As analogy, SMTP is a universal protocol and yet email giants like GMail/Hotmail/Yahoo exist. They store emails. Average users don't want to point DNS MX records to their laptops running home mail servers 24/7.

- Dropbox-the-client-software simplifies "data in flight".

- Dropbox-the-cloud-storage simplifies "data at rest".

Since storage costs money (e.g. see Amazon Cloud Drive drops "unlimited" plan), it means there would be conflicting business interests from OS vendors at that infrastructure layer. This why a company that was _not_ Apple/Microsoft /Google/Redhat such as Dropbox was able to fill a gap.

There is nothing in the world wrong with me wanting to serve 4 terabytes of content off my own local machine, and know where it is going, and to whom, without the involvement of any third-party at the content layer. That is a feasible, realistic, and tangible goal in the current state of things. Dropbox has a lot of data. They're not a file-system vendor; they're a neo-google.

Yes, thats precisely my point. Dropbox is only relevant because the OS vendors are no longer servicing their end-users needs.

I'd like to see you substantiate that claim. I see no evidence that it's true.

You can't seriously be claiming:

1. Rsync has existed since the birth of filesystems.

2. Rsync will seamlessly sync between devices in the way that Dropbox does without the use of a third party. It clearly does nothing to overcome NAT.

It seems like referencing RSync does nothing to substantiate your claim, which still appears false.