Looks like the drop in cost to get payloads in orbit, ala SpaceX and the recent Ariane announcement are gutting the market for the frankenplane.
Pegasus, the rocket mentioned in the article, is $40-$50 Million to orbit... the same price as a Falcon9. Max weight to orbit is 500kg, which is tiny; you can piggy back on the second stage of a LEO Falcon9 for a rumored $1 million per 1000Kg (Cubesats, for comparison, are usually limited to the 1-2Kg class. The new Iridium satellites, that get launched ten at a time, are 700Kg each. Iridium, it is rumored, paid $40Million US per launch.
If this thing flies paying customers? I'd be shocked. It would have kicked all kinds of ass 15-20 years ago. Now? the economics have changed and unless a miracle happens, there is no cost effective market to tap.