Nintendo is really original when naming their WiiU ports to N/3DS. Splatoon Legends will feature the full game at a smooth 30fps. Source: http://www.nintendolife.com/news/2016/04/splatoon_to_arrive_on_3ds_under_the_name_splatoon_legends
But apparently there are new game challenges and characters announced with amiibo for both 3DS and WiiU.
The highly requested Squid Sisters are on their way~!
There are rumours that Octolings will also be available.
Check out the leak: https://www.youtube.com/watch?v=d2vLFdjHgMU