This is gonna be a long one because there are so many things.
1. Bring Back Zipcaster.
It is, by far, the most fun special in the entire series. I think people generally don't want every special to just return in every Splatoon game ever, but can we make Zipcaster the first? There's several weapons that pair SUPER well with it, it's super skill expressive and has potential to be both flashy and practical, has fun counterplay, is a better backline counter than "Let's use a global special to just stop Hydra from playing the game even though I'm AT SPAWN", and most importantly, is fun enough that I wholeheartedly believe it could carry a game, both in and out of the context of Splatoon. I really want a movement shooter that uses Zipcaster because it'd be so cool.
The difference between Zipcaster and a Gmod Grappling Hook mod is that Zipcaster is fast, goes through enemies, and fucking EXPLODES. THAT IS AWESOME.
A timeline where Zipcaster always comes back like it's the fucking Purple Guy is the best timeline. A timeline where it gets used for one game, never reappears, dies as Splatoon 3's servers go down is the worst case scenario imaginable. Truly the Fallen Hero Timeline.

1. Bring Back New Squiffer
   Just... On the topic of Zipcaster, can we just copy the exact same kit over, please? Autobomb Zipcaster, Squiffer, don't want any changes to it, it is holy and pure, the combined work of humanity to create the purest balance behind practicality and fun; to destroy it is to defile the will of God.
   We will be back at square one.

2. Second kits at launch.
   I'm just... Generally gonna be pretty pissed off if I get trapped on Point Sensor Bubble Squiffer for a year, in all honesty. It feels terrible in general to be trapped on a weapon you love with a kit that you hate, I think everyone would prefer to have that variety at launch, especially since it's usually pretty easy to make a passable second kit at least. Autocaster Squiffer was an obviously great idea since S3 was revealed, I just didn't care because I didn't main it yet.
   Just, having the context of how weapons and specials work makes it easy enough to make kits that are good enough, I dunno how Reeflux Deco happens. I can only presume whoever pitched that doesn't play Splatoon.

3. Can the singleplayer maps be more in depth, please?
   I don't want the singleplayer to end up being a Splatoon Naughty Dog game, or something along those lines; so story focused that it intrudes on gameplay and replayability.
   BUT, I feel like in terms of actually delivering a story and enviornmental designs, the singleplayer has SO much room to improve. The actual level layouts themselves have been very abstract without any actual setpieces, with the exception of every game's climax. Even then, S1's climax was an abstract level with a setpiece, S2's was mostly the game, Octo Expansion actually had an enviornment with the NILS statue and general Deep Sea Metro, Alterna also had one with the rocket climb and space battle.
   I want the mindset between the last two to be used for an entire game, please. Because, aestetically, all the actual enviornmental design is typically used exclusively for the skybox.
   The way I'm thinking about it is that S1 and S2's maps - even a lot of Octo Expansion and S3's - are the old Doom games. There's just some geometry and textures, all brought together to just make something playable. What I want is Doom 2016 or Half-Life, the levels aren't just a bunch of boxes that could maybe resemble something if you squinted? They're an actual place you're fighting through, like a hospital, a citadael, a military camp, a factory, and because Splatoon actually has some really interesting worldbuilding, I imagine it could have a lot to show off. Y'know if it did.
   Same goes for the writing.

4. Can the writers finally be allowed to write?
   Again, don't want this to become a Naughty Dog Splatoon game, even if their stories are good, I don't like when my games only have a story to offer.
   But, I saw a video, "Why Splatoon 3's Story disappointed me." With the thumbnail, "Why lore matters." And in the video, it seems like the main focus is that Splatoon 3 had uninteresting lore compared to the previous games.
   My guy, we're talking about a story, then.
   Let's look at Splatoon 2 for an example, let's take out the data entires, what is it about? "Oh, Callie's missing so Agent 4's gonna kick some ass!" That's not a story, it's an excuse for simulated squid homocide, and that's fine, I play Doom, but even Doom has a bit more to offer in the modern age.
   Let's bring back the data entries, what happens now? There's an entire bit about the relationship between Callie and Marie, and how they've grown distant from each other.
   If your entire story is told exclusively in the lore and data entries, you have not told a story, you've given a good concept for one - I would say the exact same about FNAF, but even FNAF puts an emphasis on it for a bare minimum of 5 minutes. Ideally, your lore and story compliment each other, instead of being all one or the other.
   In Splatoon 2, we could've done some character work with Callie and Marie, do a bit more with them and their relationship than what was available in Splatoon 1 due to the strain that's been placed on it, but no, that's not an option because 'Fuck you for being invested in the world or characters; Our writers aren't allowed to write.'
   Just... Treat Octo Expansion as a bare minimum.
   I think Doom 2016, Ultrakill, and Black Mesa are all good examples of how this could work without 'becoming a naughty dog game'.
   This can also be applied to the playable agents, but it's less important. I don't really like self insert characters, I'd like for them to have a bit more, especially since Octo Expansion and Alterna have broken that form of immersion by reintroducing Agent 3 as an NPC. I'd prefer for the playable Agents to be actual people with real characterization instead of just "The player, if they want."
   Nobody actually likes anyone but Agent 8 for what they are, they like those characters for who they imagine they could be. Even me, my favorite is Agent 4, and I only like her because of the work I've put into making her a character in my head.
   Again, this one is fine, it's a small thing, but I have a preference.

5. Can the entire Squidbeak Splatoon be present?
   That was in the concept art for Alterna, and it's massively disappointing that it didn't happen. Especially if we never get to see them again after this game because 'We want to do new things.' As if they did a lot with with Squidbeak in the first place. All I see looking at the actual stories of the Splatoon series is wasted potential.

More feminine clothing options, so far we only really have the school uniforms.
More Octoling hairstyles, Inklings have twice as many, and that's racism.
More map gimmicks, please. And, hopefully, less annoying gimmicks.
Easier way to get ability chunks, considering how important they are to identity in the game.
Ability tester so we can get a better idea of how they impact the player instead of looking at a spreadsheet and imaginging it.
Endless salmon run mode would be very cool, probably a survival mode. I have several ideas for how to balance it.
Please don't make Deep Cut and Off the Hook Squidbeak agents.

Uh... thx for coming to my tedtalk, k bai-