Development of a manned spaceplane by the military would require a budget comparable to the development of the B-2 bomber (i.e. somewhere around ten billion dollars for R&D alone--about half what the Shuttle cost to develop in today's dollars). That kind of increase in black budgeting would show up unless this thing had been in development since the 1980s.
Second, boron-based fuel is notoriously unsuitable for rocketry, not merely becaue of its toxicity (the waste products are considered to be an internationally banned chemical weapon), but also because it is a paste--too thick to flow through any sort of pump, but too soft to mold into a solid rocket motor.
Third, I don't care what fuel it uses, because if it's powered by chemical rockets of any sort, it has to have a fuel/mass ratio of about six to one (i.e. the fueledass must be sixmes as heavy as the dry mass) to make it to orbit if it is dropped from a plane at Mach 2-3. It's going to need to launch with drop tanks.