Local Artboard Editing Mode
Illustrator already notionally works on one artboard at a time... the one that's zoomed to with Cmd-0, or pasted to with Cmd-V...
Perhaps there could be a mode switch, similar to the 'Draw Inside' mode where all operations are confined to objects on the current artboard. Useful for Cmd-A for example. This would override unlocked artboards of course!
This mode of operation is already familiar in InDesign where only current spread-object appear in the Layers.

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This feels like a less-frightening way of introducing artboards-as-pages / layers-per--artboards, requested here:
http://illustrator.uservoice.com/forums/333657/suggestions/31133392I like your idea and do really wish for it to get more votes.
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A related request:
Real Isolation Mode
http://illustrator.uservoice.com/forums/333657/suggestions/44535912