Well, it looks like maverick designer Burt Rutan has done exactly that.
He and his company, Scaled Composites, have worked on bleeding-edge launch concepts like the DC-X, the Roton, and NASA's X-38 -- all of which got canceled. Now, they've taken the old concept of launching a spaceplane from a manned aircraft, and built SpaceShipOne and its launch vessel, The White Knight.
That's right, built. Not just designed or modeled -- they got private funding and built an actual airworthy vessel in two years.
Now they just have to prove it spaceworthy. The launch vehicle has flown several times, but they haven't tested the space ship yet. I hope they pull this off -- it could really give a kickstart to manned space flight.
And watch out for those cosmic rays, guys.