The problem with Dyna-Soar is that while it was a brilliant vehicle, ahead of its time, it wasn't really usable for any plausible mission - for either DoD, or NASA. Which of course is why McNamara cancelled it. NASA could have taken it over, but then it would be faced with a one-man (sorry, person) vehicle with limited life support and power, and no docking hatch. What does it do with it? It's terribly inconvenient for use in an EOR lunar architecture but for anything else, too - like access to a LEO station. So NASA would have to upscale it to at least three crew, and stick a hatch on it, for starters. It could perhaps have evolved into the role that the Space Shuttle assumed, in time - at least in the crew transport role. But it would have required a lot of development to make it into something NASA could actually have used, and there's no way that could have been done in the context of a race with the Soviets to put men on the Moon. Lunar orbit rendezvous was chosen because it really was the only realistic way NASA could have beat the deadline.