Uh, maybe. IME well-designed carbon frames are also well-damped. For that matter, our steel Speedster is damped plenty well enough not to tire us on long rides. Be that as it may, IME Santana is correct about the role bike weight plays on a long ride. But . . .
We call it "position." Well, it's not new and it's not really technology, but it's how you really can go a lot faster. We use aero bars for both captain and stoker, even on rides with lots of climbing. It's only 2 lbs. Anathema to the weight weenies, but like Santana says, weight weenie isn't really how you go faster. I don't know if there's proof that Bilaminate Damping will make you faster, but there sure as heck is proof that aero will make you faster. It's free speed. The captain's position must be the usual roadie position, bars below saddle as far as the frame allows. We use a slammed -17° stem. Stoker must be completely hidden behind the captain. This may require a longer stoker compartment, depending on the stoker. Ideally, stoker should be able to rest her forehead on the captain's saddle, or close to it. Slammed stoker drops can work. We use a set of stoker aero bars, with stoker's hands beside the captain's butt. More comfortable for stoker and more aero than drops.

So if I were having a new tandem built, that's the direction in which I'd look: aero. Lightish but stiff and well-damped carbon frame and fork, aero carbon wheels, discs, short head tube, for us a more slanted top tube to drop stoker's stem further. Stock BB spacing is OK for us. We like our conventional triple/timing belt or chain componentry. I'd probably spend the weight for couplers. I'd want touring and fender brazeons and a fork that would allow 28mm tires for touring. We'd put on our clip-on aero bars just like we have now or maybe something fancier and carbon.