Sakurai, the Director of Software Development for Sora Ltd and Project Sora has posted on his Twitter account that he has been browsing the Smash Bros. Dojo as part of his research into development of the next Smash Bros game. Back in June 2011 at the E3 press conference, Satoru Iwata of Nintendo announced that the next Smash Bros game would be developed for the Wii U and the 3DS, and that the two games would work together in some form. Sakurai-san stated that work on the next Smash Bros would not begin until his latest game, Kid Icarus: Uprising was completed. That game went gold in January, which signals that the next game could very much be underway.
Metroid has had a presence in every Smash Bros game since it was first developed for the Nintendo 64. Samus Aran has always been a playable character and in Super Smash Bros: Brawl, Zero Suit Samus was added as a playable character. There is no reason to believe that this trend won’t continue, and we should see some Metroid love for the next installment of the Smash Bros series.