For those that haven't seen Freespace 2, here's a video. Ignore the German music and have a look at the beam cannons in the background. That is what Yurch and I are taking about.
http://video.google.com/videoplay?docid=2135158499288360164&q=freespace+2&pl=true
I have to agree with yurch here. Yurch and I are constantly using the Ion-120mm combo to devastating effect. A Freespace style to the ion cannon would make it more of a challenge and more fun to use.