First we need to start with space itself, which is still misunderstood. I propose that the Universe is divided like oil and water so to speak, matter/ dark-matter/anti-matter. There are umbilical cord like, electromagnetic tunnel/wormhole connections emanating from the core's of all bodies from smallest to largest scale. Galaxies are connected to other galaxies and are core locked through this process. Because of the flow through these tunnels/wormholes it could work against or for your engines. This Em Drive works on a rotating magnetic field, which not only propels the craft forward but protects the ship and passengers and provides the magnetic that is critical for humans for long term space travel. Advantage of this setup is that when you are ready to start slowing down you just reverse the coil flow, through the stationary non-moving dual rotating helical coil array, to start slowing down.
A deep spacecraft that wants to travel across an area that is dark-matter will require an opposite field than traveling through an electromagnetic tunnel/wormhole. An Em engine of the coil type could also adjust its field to work in both environments, in theory at least. This I see as the future for Em travel. I propose that if we could shrink down and fly around an atom we would in-fact need an em drive and ship that could work in a very low or negative electrical state and a positive state to visit all that is inside that small microcosm of space.
New to forum hope it's in the right place. I'm in extreme pain, and Hope I need not reply. "May truth find your mind fertile when you find it" Lowell D. Williams