Daimler's official press release only points out "(some of) the features that distinguish it from the standard-production models include extra spaciousness, special seats and lavishly designed, prestigious interiors offering extensive scope for individualisation."
No word on special exterior features whatsoever (expect implicated longer wheelbase & thus different roof line & silhouette). Although - being a sub-brand like AMG - it can be expected the Mercedes-Maybach to feature some special exterior trim: eg. different grille, slightly different front & rear bumpers, possibly different rocker panel, exclusive wheel designs, extra exterior chrome trim details etc. But I don't really expect bespoke light (headllight or rear light) designs. It looks like the main extra features of M-M sub-brand are concentrated in the cabin - especially in the rear since the car is catered to rear passengers.
IMHO it's a smart move. S-class is an icon. Yet with 100,000+ annual sales it's hardly exclusive therefore Maybach & Pullman editions make sense. Although both of them can't really compete with Bentley & Rolls-Royce & Aston Martin etc. But they will definitely push MB (and S-class especially) brand much higher than BMW, Audi, Jaguar, Porsche, Lexus and even Maserati.
I have always been found of the sub-brand idea. I would push it even further: Mercedes-Daimler for commercial vehicles, Mercedes-Benz for core Mercedes passenger models, Mercedes-AMG for Mercedes sports cars, Mercedes-Maybach for Mercedes luxury cars (I can easily imagine a Maybach version of GLS), Mercedes-Pullman for Mercedes ultra-luxury cars ... and ultimately: Mercedes-smart for Mercedes innovative & funky vehicles, expanding smart sub-brand much beyond micro & mini cars.