There was a lot of talk about it back in '06 when the news came out, and how it could reach a specific impulse approaching 20,000, but I haven't heard any updates on it and the ESA link doesn't work. Anybody know if it's still being worked on and if it's something viable for in-use production in the near-future?
It seems like there isn't any serious work on the table relating to it. I was able to find a recent article talking about it, but it doesn't seem to contain any new information.
The great limitation of this system is that it requires a lot of energy. It was developed in 2005, which was an interesting time in the development of high power spacecraft, namely the Jupiter Icy Moons Orbiter, a nuclear powered spacecraft that was a concept from 2004-2005, when it was cancelled. Although JIMO had it's own ion propulsion system HiPEP, I suspect this engine was developed as an alternative. Currently, no spacecraft in planning has anywhere near the power to even consider using DS4, and so it doesn't make much sense to continue to develop it. 250 kW is a lot of power, far more than any spacecraft in existence currently uses.