as you surely know, boeing acquired md years ago, so any new "md" aircraft would carry a b-7x7 designation (vis-a-vis 717).
i think i've seen a couple the md-12 design concepts years ago, a double-decker (not unlike the 380) and an -11 stretched to a ridiculous lenght among others -- md's last-minute desperate attempt to breathe some life into their long-haul orders they've watched slip to boeing.at any rate, they're history now, as is any jumbo-transport effort by boeing - with airbus taking over, we're one step closer to a pilot-less cockpit...