I don’t think the next quantum leap is going to come from ejecting mass opposite intended direction of travel.
https://en.m.wikipedia.org/wiki/Fusion_rocket
The mass problem is not really a problem because such a rocket wouldn't be trying to have perfect magnetic confinement, which is only necessary if you're trying to make a net gain on electricity flow out of it. Jetting out some plasma requires imperfect confinement, so there's automatically no mass problem.
Discussion
That's not even what we do now. We calculate paths of least action and eject mass efficiently. There's precious little one can do to sidestep the principle of least action. The next quantum leap might just be ejecting mass in a much more efficient direction, via a network of booster terminals spread throughout the solar system that respond to price signals and requests for use as a gravity slingshot, a refuel, a booster burn, etc.