If the Carrera GT makes it into production, it will most likely make a better tranformation than the Boxster did from show car to production. The Boxster ended up looking like a 70% copy of the show car shown in '93 (and which had me nearly going into convulsions when I saw it in C&D

). The reason for this is b/c the Boxster show car was released at a time when Porshe needed something to get the public's attention. Remember, this was before the restyled 993 Carrera came to market and before Porsche started rolling in $$$ again. They also took more liberties with styling elements (such as the low mounted side scoops for engine/brake cooling) and the rear lights which were faired into the rear fenders (expensive to produce then, yet now seen in the rear tail lamp design of the PT Cruiser). The production Boxster ended up looking a little "flatter" than the concept car, but it is still the best looking roadster on the market.
IMHO, the Carrera GT will see a transformation from show car to production car much like the Audi TT. The Audi TT made the change from show car to production looking like a 99% copy. The only giveaways are the ever so slightly enlarged bottom front air intakes, and the reshaped side glass/canopy (for better visbility). Other than that, the Audi TT Coupe and Roadster look EXACTLY like their concept counterparts
Porsche has nothing to prove now. They are on top, they're raking in the money, they've got great looking cars, and they even have a cash cow SUV coming. I believe that the Carrera GT will therefore stick at least 95% to the current shape of the show car. The only possible details that I can see them changing are the interior. And I also don't think that Porsche would have developed a "one-off" V10. That just doesn't make sense. Money gone down the drain IMHO. Usually, when a show car showcase a new engine, it shows up in future model lines. i.e.
'89 Dodge Viper 8.0L V10- '92 Viper RT/10, Dodge Ram
Ford Indigo, Ford GT90 6.0L V12 - Aston Martain Vantage
Dodge Copperhead 2.7L V6 - base Dodge Intrepid/Chrysler Concorde, Stratus Sedan, Sebring Sedan