According to Japanese Mac blog Macotakara, the iPad 3 will be backwards compatible with current Smart Covers, despite the fact that it will be so thick as to not work with iPad 2 cases.
Macotakara claims that they don’t know the reason the iPad 3 will be thicker than the iPad 2, but we do: it’s necessary in order to install the twin-light system needed to lluminate the iPad 3’s Retina Display.
As for the image above, your guess is as good as ours. Macotakara seems to think it somehow relates to an iPad 3, so maybe it’s the unbranded aluminum back panel of one or something? As for the Smart Cover backwards compatibility, considering that all that is necessary to keep a Smart Cover on are magnets in the right places, I wouldn’t be surprised if Smart Covers continued to be backwards compatible for future iPads for many generations to come..