Most likely. It will be a mystery game where you have to figure out whether you are a kid, a squid, or both. I would like to see a portable Splatoon as well, but that's likely if the NX is a fusion console.

Considering the great sales it's been having, I'd be more surprised if we didn't eventually get a sequel.

I think the better question is:

Will they actually call it Spla2n?

Maybe a spin-off with more stealth elements and a darker vibe.  Splatoon: Black Inks.

yes it will and it will probably come to 3DS or a spinoff atleast but a sequel will happening

Or Splatoon: Beach Volleyball, with only bikini-clad female inklings shooting creamy white ink at the ball and eachother...

i think Splatoon 2 is going to be on the next Nintendo platform, maybe NX. but it will definitely get a sequel

You dont belong on this site if your asking questions like this. What in Yevons name would have you think Splatoon would be one n done?

You guys are good. 

Yeah, it'll prolly get a sequel. There is a lot of room and potential for this series to grow.