Darwinianevolution on 15 November 2015
I don't know. Depending on what they'll say in December, Nintendo might make a Special NX Edition, with all the content and DLC avalible from the beginning. If they wanted to make a full new Smash, they'd have to start now, and Sakurai wants to work on other things.
Also, a good question is, when will the 3DS be discontinued? I can see Nintendo supporting both WiiU and NX versions, but the 3DS one is quickly becoming a hindrance. We could recover the Pokemon Trainer, the Ice Climbers, and other characters like that the moment the 3DS version gets dropped, but they have pushed it as much as the WiiU version.
