From an interview with 4Gamer:

http://nintendoeverything.com/splatoon-2-producer-on-the-setting-weapons-stages-gear-single-player-campaign-amiibo-online-more/

- Due to data optimization, there will be less lag and connection errors compared to the first game

- Some stages from the first game will return, but with new elements 

- Amiibo will be supported

- Since 2 years have passed since the original, styles and trends have changed in the squid world

- Single player campaign will have around the same amount of content as the first game

I have high hopes for this new Splatoon 2 game! All we seen was a demo with 1 stage and a trailer.. makes me think how awesome the full game will be like! How awesome will the music be like? How much addiction will this game cause me? I DON'T KNOW it's exciting!

Splatoon 2 is gonna be so good, from the looks of it, it's everything I wanted in Splatoon's sequel! I hope it has as much replayability, constant updates, free dlc and splatfests made Splatoon last a long time, I was playing over a year later still with new content to enjoy!

Looking pretty good, in regards to those "New elements" it's likely old stages with those things from the first campaign like the sponge and those ink rails, the latter we saw in the trailer.

But yeah, excited!

I just hope it has split screen co-op for online MP.

Can't wait to play this on the go!

Glad to know there is another single campaign but I would rather have a longer one this time, oh well, I really liked it on the first one.

Yeah, while I would've preferred it to be a bit longer, I actually loved the first game's campaign. In fact, as someone who isn't into online multiplayer, I found Splatoon one of the best games of 2015 on the strength of its single player alone.

Has Nintendo confirmed additional local multiplayer options?

I can understand it, the game was so refreshing, charming and fun even on its single campaign. Then in the multiplayer was just epic, worse than drug, Splatoon is still my favourite game of the gen.