No, that depends on the theme. It is perfectly ok to put one "sidebar" on top or at the bottom.
Indeed. You can put both of them wherever you like, it's only the admin interface and class and ID attributes that refer to 'sidebar', 'right' and 'left'.
This isn't some future functionality, it's available right now, and these terms are already out of date.
+1 on Region
Yes, but it will still be called 'right' and 'left' in the block admin interface, and that is the point.
All that shows is that we need to rethink the block admin too :) Block-region-1, Block-region-2?
It's going to be more confusing isn't it - we're back to the usual tension between making it powerful and flexible vs making it easy for novice admins...
Unless someone comes up with some names in place of 'left' and 'right', this discussion is going nowhere. Goba