Here's a few more stupid thoughts I've had:
A weapon that cannot spread ink. Like, at all. It just shoots people.
A weapon that splats in 5 shots (6 with any Defense Ups) and fires 2-shot bursts every time you tap ZR with no rapid-fire. With a slow fire rate and Inkbrush range (kinda like an anti-Nozzlenose). And a very wide spread. And its sub-weapon is the Point Sensor and its special is the Bomb Rush (Point Sensor Rush? I can't come up with anything worse than that for a special).
A special that just refills your ink. Nothing else, just a refill.
A special that lets you tap the GamePad map to shoot mini-Inkstrikes until your special gauge is empty.
Enemies being able to get your Bubbler if they touch you, like how teammates can get Bubbler by touching you.
(Okay, I'd actually kinda like those last two, but that's probably just me)