I think there's some gimmick ideas that could be done.
@OnePotWonder had some ideas about a limited ammo shooter I really liked but instead of running out of ammo completely, maybe you'd get an ultra powerful fire, like a high fire rate accurate good painting 3-shot, that gets a big fire rate/range nerf after firing for one second, or a buffed .52 gal with perfect accuracy, slightly better range and better paint, that also gets slower after one second. But you'd be able to recharge your high firing mode by not firing for one second.
Hell, in a way this could be a better alternative to shooter rng, since it follows a similar ruleset. I actually think it could make for a more fun .52 rework on both sides.
I don't like messing with damage numbers though, inconsistent damage isn't that fun to play around.
I'd also like to see a spray shooter with a perfect accuracy jump mode, a horribly inaccurate ground mode, that immediately starts as inaccurate, and a high fire rate, but mid ink efficiency (Chara has NEVER talked about this for aerospray I promise). It'd honestly be a really cool short range shooter support alternative, since you'd get even better paint, but you'd be more vulnerable to getting rushed down since you have to jump to defend yourself. But the jump mode would still give you a way to defend yourself better than poor little spray shooters over there.
I think it'd need the jump mode to be some kind of longer ranged splash, to make sure it's worth being aggressive with. It needs to be worth using so the weapon doesn't just play for paint spam.
You know what, make it heavyweight, just to make sure it can feel like a powerhouse, make it a high skill support weapon.
I can think of a few ideas to be done with new gimmicks, but it's true that it's hard to imagine a new 'straightforward' shooter. You could mess with lag, besides .96 there isn't many shooters with noticeable lag. I'm also curious to know what a shooter with a bigger hitbox would give us, that's kind of unexplored. But it's inevitable for it to be compared to preexisting ones really.
And to be honest, I would not be opposed to the two ideas I mentioned to just be some kind of .52 and Aerospray rework.