Depends pretty much completely on how well the NX is received.
I think we need to wait and see if it actually has legs in North America and Europe too. It definitely is showing signs in Japan, but the US and Euro markets are very different and much more fixated on military or sci-fi shooters and that could hurt Splatoon here. It had a decent start here, but it should have sold a little more I think because there are more Wii Us in the US than in Japan but that wasn't the case, so that would seem to indicate it could be bigger in Japan than the West.