I haven't seen much speculation about another TAM, like the Twentieth Anniversary Macintosh:
http://www.apple-history.com/?page=gallery&model=anniversary&performa=off&sort=date&order=ASC
I'd wouldn't be surprised to see another limited edition, expensive, "collector's edition" computer.
My guess would be an iMacIntel in a black anodized brushed aluminum case, with better graphics, 4 GiB RAM, 500GB disk, and maybe some other surprises (like the CPU heat piped to the aluminum case so that it was much quieter).
Maybe even move the power supply to an external brick so that it could be fanless - and eliminate most of that ugly blank space below the screen.
Include a coupon for a free upgrade to a Merom in the fall.
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Come on, y'all. Think different for the 30th!