Interesting but extremely expensive and dirty. The reason for cancelation, correct me if I'm wrong, was that same expensiveness and pollution of near-Earth space by explosions of the nukes.
On the other hand, once made, it could have become by itself a comparatively cheap (taking into account acceeration, mutiple usage and capacity) interplanetary shuttle probably capable to bring all necessary materias and speciaists to start colonies on the Moon (mining and industrial bases) and around Jupiter (to start project "Daedalus").