Honestly, no. It's releasing on the same platform so there's nothing it will do that couldn't be done with more Splatoon 2 DLC. But that wouldn't make them as much money. Sadly, Nintendo has fallen into that trap so many others do when they start seeing dollar signs. Just like CoD and Fifa and others, they're releasing new games with minor changes just to maximize their profits. I thought Nintendo were better than that, they always seem to innovate or change things up in some minor ways but it's enough to make it feel fresh.
I'll probably end up having to buy it though, because I had fun playing Splatoon 1 with my brother, and he skipped 2, and is thinking of getting 3.