That makes me wonder whether Safari extensions can access iCloud Tabs. If so, it'd really come in handy to be able to do things like "move all these tabs from this device to this device". I accumulate tons of tabs on my mobile devices that I'd like to move to my Mac (or vice-versa, depending on circumstance) so I could just crank through them all at once.

[Edit: A brief look makes it appear that native OS X apps can, not sure about Safari extensions. But a native app could be sufficient.]