I like the idea of it being a super-capship heavy bomber. Higher speed, slightly more maneuverable than the typical heavy bomber but light on general offensive capabilities. Rather than engines those could be two large, fixed, beam turrets. Only two primary gun turrets with only a couple of supported primary weapons and it can't carry bombs or any type of tracking missiles (heat seeking and dumbfire only).
It wouldn't do much against fighters but a wing of these things would be great against Shivan juggernauts. With the way that FS2 ended I would think that command would be looking for better ways of combating Sathanas class ships than just relying on the Colossus. That is if this were actually intended for FS2 universe missions anyway.