Well Moto typically have used a carbon-fibre effect on their kevlar backs, so that's not much of a stretch.
TBH I don't think you can fit that big a battery into something that thin (without making it larger in other directions). But a bit of taper at the edges to help the hand fitting wouldn't be a bad plan.
I'm hoping less bezel than the RAZR HD, but doubt they'll take it quite that far. And TBH I hope the 4.8" rumour is correct rather than 5", with minimal bezel to keep the handset size down.
But yeah, that's a sharp looking concept.
Won't be real, but I like the thinking - to do what Moto want this thing has to be attention-grabbing, so I hope they are thinking about this sort of thing.