In an alpha gameplay trailer you can see a version of Splatoon's 'Port Mackerel' map, as well as several player and weapon models taken straight from the Wii U game. I'm not sure Nintendo will be all that thrilled about that, but nothing's been taken down yet.
The paint itself still needs some work. Players can dive in and swim around in it, but it currently spreads across the map in clunky squares, rather than the more natural splatters found in the original game. Still, the basic idea is there, and you can turn intoat any time.
As the team explains, "Any and all Splatoon assets used in this mod/video are ©Nintendo and is used without permission," so I would imagine Nintendo's team of lawyers are currently sharpening their cease and desist orders.