I saw there was an update to the dev app this morning and I thought I'd take a look at what's in there, aside from matchmaking which is a whole other topic, there are some new engineering tools and ammos that I think can make gunners more useful. I like dragon ash and would like to see that make it into the game, but that's not necessarily going to make gunner more useful. Mostly I'm looking at the shield buff tools and "armored rounds", I think. I could be mistaken with regards to how the shield tools work, but it seems to me a gunner could use that on the main gun to A) help keep the main gun from going down during merc/art assaults and B) allow a goldfish to ram without losing the front gun or make the spire a little bit more survivable.
I also want to take a moment to reinforce the idea that was brought up earlier about passive gunnery equipment. Something like an adjustable scope or joint/bearing grease. Those could make gunners a lot more useful in a lot of situations where a light gun only really benefits from 1 ammo type.