For walls, I'm thinking that it would block the player from buying the weapon that makes it easier to deal with a certain kind of Salmonid until the player has defeated the required number, an example being the Explosher not being able to be bought until a certain number of Flyfish has been taken down when you destroyed at least one of its baskets with Splat Bombs.
How about...no skill locks for weapons at all?
Seriously...all skill locks do is shut out the majority of players from the full functionality of the game. Hard pass!
I was thinking what would be cool is instead of having a wall on weapons Nintendo put in Customizable gear with stickers for gear and weapons.
After defeating meeting certain monthly challenge goals you will recieve stickers (with designs similar to he mem cakes, with character emotes, brand, etc.)
These stickers can then be put on special gear unlocked in the mode or added to the grizzco weapons (which would kinda be like the hero weapons but fully customizable design based on the sticker you collected)
It would then encourage completing the challenge while encouraging completing challenges
Speaking of I would love to see an 8 player co-op Salmon run mode, with larger maps and smarter bosses that will require cooperation to take down.
But it require improvements to the internet functionality to work well.
Lastly....
I want a map designer, after smashbros map maker, and super mario maker direct I feel like it would be cool to have custom maps (that are monitored) in Splatoon 3.
These wouldn't be online neccesarily but rather be playable in private custom lobbies (with popular maps showing up in turf wars or maybe even in splatfests)
Anyways those are just some thoughts I had recently just to build on the customization and creativity of splatoon