Undo dual squelcher's removal! I consider dualie squelcher's addition to be a separate change from this, though, so it shouldn't remove that weapon. Today, dualie squelcher would probably be an interesting fusion of splattershot nova and splattershot pro: less damage and accuracy than pro, more dmg. and acc. than nova, less paint, mobility, and ink efficiency than nova but more than pro. Has both support and slayer characteristics, but doesn't really excel in either (jack of all trades, Master of none.) Its well balanced attributes make it the one shooter I sincerely care about though.
Honorable mention to the X rank lobby emote from S2 not being present in S3. Could even convert it to an actual S3 emote rewarded for unlocking X battle/reaching S+ or something.
There's probably a couple of other things, but I can't really think of anything else.