Sure, I'd like to see new subs and Specials. The current selection is fine, but it could be expanded without being too problematic. I think they could be added, though perhaps the lack of distribution relative to the subs the game started with could be annoying.
As for what I'd like to see, I'd like to see variations on the current subs and Specials.
For example, I'd like to see a kind of Sprinkler with Splattershot Pro distance on its shots and a faster fire rate, but which only covers a not-very-wide (a little wider than one of Saltspray's walkways) conic area, which could serve as a sentry-esque weapon to keep enemies at bay or attack foes in corridors while you do something else. Seems like something that could be fairly useful in Splatoon, at least to me.
As another example, perhaps a sub that deals little damage, but cuts the enemy's ink tank by 50% if you hit them with it. Not sure it'd be useful (maybe the ink-loss should be higher, but I'm afraid it'd be too powerful if that happened), but it would probably be extremely annoying to deal with, so I'd like to see it, if only on one or two weapons.
On a similar note, maybe a sub that prevents you from using your main weapon (so, pressing ZR does nothing) for a few seconds if you get hit with it, like a Disruptor for guns/rollers/brushes instead of for Inklings. Would be very annoying, especially on weapons with no attacking ability outside of their main weapon, like the Dynamo Roller, Custom Splattershot Jr, or .52 Gal (yeah, Killer Wail is an attack, but it's so slow that it's probably not going to matter if you get hit by this sub), or weapons whose only attacks are ZR and Specials, like the Krak-On Splat Roller or Custom E-Liter 3K. Would probably neuter Chargers too if you got close enough to land one (especially Kelp Splatterscope/Splat Charger and Classic Squiffer, but I could see E-Liter getting messed up a bit by this as well).
Also, for a completely new to Splatoon sub-weapon (since they should do more than just variations of current weapons, at least that's how I feel), I'd like to see some sort of ink-blast-jump that would be higher than your Inkling's normal jump. You could use it to reach higher areas and damage nearby enemies (not a one-shot unless you're right next to them, generally more of a two-to-three-shot). It's more of a utility thing, the utility being the ability to jump in midair and jump higher than your normal jump, allowing you to reach otherwise-inaccessible areas and shortcuts. It would drain roughly 65% of your ink; high enough to prevent consecutive uses on a single ink-tank while still being low enough that you still have quite a bit of ink left afterward to ink the area you just jumped to. Additionally, the ink-blast-jump would propel you in the direction you are facing, even if you are not moving in that direction while in midair. This could be used to escape dangerous situations or just avoid falling off the stage. I'd really like to see this one. Maybe on an Inkbrush?
Also, I'd be interested in seeing the Inkstrike from the first trailer return (the one that looks like a giant ink-bubble slowly expanding and being filled from the sky by a small ink-waterfall-thingy), though instead of just covering turf, it could create a large ink-bubble (like it does in the trailer) that expands for a second or so, then stays in place for a second or two, and works by preventing enemy ink from passing through and pushing enemies away (while your teammates can enter and exit as they please), but can only do minimal damage with the bubble (like bumping into the Rainmaker's shield), though if you're hit by the ink-line falling from the sky you'll be splatted instantly (but that's really small, so it's unlikely). It's essentially the inverse of an Inkstrike, with a bit of Bubbler thrown in; inking turf poorly, but creating a shield in which your teammates can act with impunity briefly. It would be aimed and activated like an Inkstrike, allowing to place it anywhere on the map (like, say, a Splat Zone), but it would be a bit smaller than an Inkstrike in size.
Another thing I'd be interested in seeing is a Special that prevents enemies from charging or using their Specials for a while when activated, like an Echolocator that screws with your Special meter instead of revealing locations. Cold-Blooded would cut this Special's duration, to balance it (if it works for Echolocator, it should work for this).
On the same tack, another thing I'd be interested in is a Special that cut all enemy Special meters by 50% of the gauge, even if it were already in use (so your Bubbler/Inkzooka/Bomb Rush/Kraken duration just got a lot shorter, and if you hadn't popped your Special yet, you just lost the ability to do so). Not sure if this would be balanced, maybe if Special Saver lowered the Special loss (would make sense, at least to me).
That's what I'd like to see. Not sure all of that would work, but I'd still be interested in how the game would change with any or all of these in play.
I would like to see more non-standard Sub/special pairings, though.
Also this. Just so long as they don't do Point Sensor/Echolocator (just seems redundant) or Point Sensor/Bomb Rush (why).
Splash Wall Rush would be interesting to see (though probably extraordinarily annoying to deal with), and I'd like to see Seeker Rush in particular on more than one weapon (especially since I don't like putting it on the Carbon Roller; maybe it'd be better on a Splatling or a Slosher).
Right now, no. New weapons will be fine but i'd imagine adding too many subs and specials would make it too convoluted for people new to the game. Plus it'd mean that all of the older weapons wouldn't have any of the newly introduced subs and specials, meaning it won't be that widespread as the existing subs/specials.
Maybe for the sequel would it be a good idea!
Definitely for a sequel, but there's quite a bit they could do right now if they wanted.
Still, they should hold some ideas back for Splatoon 2.
And yeah, weapon distributions of the new subs could be a problem. Maybe just make a new version of a bunch of the older weapons with the new subs and Specials (or a new sub and old Special, or an old sub and new Special), like a Cuttlegear Octobrush or a Squiffer Deco or KOG Dynamo Roller, that sort of thing.
They still wouldn't be as widespread as some of the current subs and Specials, but there would be more than one weapon option for people who wanted to use them.