There was a fan attempt, EP I think you contributed to that, I have a vague memory of being involved myself, to rewrite the Centauri fleet list with ion cannons instead of battle lasers.
The thread title is 'House rules for Beam-less Centauri', I searched and found it but- how d'you post one of those things anyway?
Replacing the twin arrays would be interesting; RBax gives stats of range 24, AP for an ion cannon in First to Fall.
I've always found Twin Arrays to be basically weapons of opportunity in the offensive role, and pretty shabby in the defensive. They're not something you really bust a gut trying to get into range with, are they? Replacing them with Ion Cannon would give the Centauri a secondary of genuine tactical value, slightly outranging even the Minbari. I'd enjoy that, but the howls of protest from all over the boards might be a bit too much.