Sakurai has said Super Smash Bros. for Wii U is likely to be the final Smash Bros. game developed by him.
I hate to see Sakurai leave the series, but it gives him more time to work on other games. Kid Icarus: Uprising was amazing, so I'd like to see another non-Smash Bros. game from him. And I don't doubt Nintendo would release another Smash on their future consoles without Sakurai being involved. There's definitely going to be another Smash game, even if Sakurai isn't working on it. If anything, it makes the possibility for more characters, it's Sakurai's fault we still haven't gotten Ridley playable yet.
I can't positively declare there won't be [another Smash Bros. game]. With both Melee and Brawl, I made those games with the thought that there wouldn't be any more sequels. Thus, I really can't deny the chance for another. However, as for myself, I don't think there will be. In terms of scope, and in terms of sheer number of characters, we went beyond our limits long ago, and yet, if we cut the number of fighters or modes in a future game, I'm sure there would be complaints. You could say that all the effort in the past to stretch out, keep pushing myself, and provide all these extra merits wound up tightening the noose around my neck in the future, that may seem like it contradicts my personal desire to keep giving gamers as much as I can, but I don't see any easy answer for it. And yet, despite that, I also have trouble picturing someone else taking my place and providing all this value-added content without me.
I hate to see Sakurai leave the series, but it gives him more time to work on other games. Kid Icarus: Uprising was amazing, so I'd like to see another non-Smash Bros. game from him. And I don't doubt Nintendo would release another Smash on their future consoles without Sakurai being involved. There's definitely going to be another Smash game, even if Sakurai isn't working on it. If anything, it makes the possibility for more characters, it's Sakurai's fault we still haven't gotten Ridley playable yet.