Requirements:
* It should only deal with filesystem operations (i.e. SSH is way too problematic).
* It should be firewall-, NAT-, proxy- and browser-friendly.
* It should have cross-platform servers and clients, fully operational via CLI as well as GUI.
* it should be secure (i.e. no http, thanks; https, maybe.)
I'd say it's potential startup territory, except I cannot see any monetization opportunity. Also, the usual XKCD on standards: http://xkcd.com/927/