Nah, other people still use this. I do, when I'm not trying out new weapons or using the N-Zap '89. And Splattershot Jr. is hardly forgotten, I see plenty of them online.
Unless you mean the Custom Splattershot Jr. That has been thoroughly forgotten.
I've had quite a turnaround of thought (did that make sense?) on the Nozzlenose. It's actually quite good, like a Blaster except different (in my opinion, anyway). It's easier to cover turf and get around with this (relative to the Blaster) since it recovers from firing so quickly (is it really 8 frames? Because holy s***), and the relative lack of power is compensated for by the speed. And on top of that, it has pretty good range. Its loadout fuels the Blaster comparison, since it's the same, and the Nozzlenose benefits in similar ways. Disruptors let you slow opponents so you can more easily hit them, which is arguably bigger for Blasters (1-shot weapons in general benefit heavily from Disruptors, so I'm not surprised the regular Blaster's the only weapon of its kind with it), but the Nozzlenose's superfast fire rate makes it a great candidate for this as well. Both benefit equally from Killer Wail's long range and through-cover attack, though the L3 arguably needs it more for bunker-busting (since it can't do 1-shots like the Blaster can).
Actually, I take back what I said about this being a better Blaster (well, not entirely). Between the very rapid burst-fire, the ability to shoot off bursts very quickly, the respectable-but-not-great power, the good range and the good turf covering ability (am I the only one who feels this way about the L3?), the L3 Nozzlenose is what the Rapid Blaster wishes it were.
Of course Disruptors are underrated, they're on so few weapons, and not without reason; it really is overpowered, the ability to slow enemies in a game with such high damage is insanely good. If this got on, say, a Roller, that would be the terror (especially a Dynamo Roller).
And personally I've always wanted it on a Squiffer-esque Charger, just to see if it would be good.