I mean, I feel Graal could probably get away with it. Things can be similar and not get copyrighted. But there must be a good difference between them which I feel Graal has enough of in differences assuming 3D would be like Classic,Era,West,ect.But this is Nintendo afterall... They are pretty sue happy, Will even try to take down videos of gameplays of their game's, Or they'll take 90% of any ad-revenue you'd get or even more, So I wouldn't push it.

More so surprised they're using unity more than anything right now, given how crappy that game engine has proven to be, Especially MMO ones, But i guess it is better than Torque3D, Which is somewhat an improvement i suppose? gonna wait to see how buggy this'll be, Maybe first good unity game in a while idk