The gang over at Source Gaming are working on a translation of a Famitsu interview with Masahiro Sakurai. While no specific upcoming projects are mentioned, Famitsu does as Sakurai how much longer he'll be making games. You can see his statement below.
…Well for me, every time I always think, “This might be the last one.” If it’s a request from a client then I’ll consider it, but I do wonder, “Is it alright if I’m not the director?” It might be good to take on more of a consulting role.
What does this mean for the future of Smash Bros.? I guess if Nintendo asks Sakurai to take the project on, he might consider it. That said, it seems like he'd like to take more of a backseat in the development process moving forward, no matter what the project is.