Shigeru Miyamoto spoke to Eurogamer and announced that Pikmin 4 is in development. "It’s actually very close to completion. Pikmin teams are always working on the next one," Miyamoto said.
A platform for Pikmin 4 was not announced. While Pikmin 4 could be a Wii U game like Pikmin 3, Nintendo also has a new console, the NX, which will be revealed next year. Perhaps Nintendo will have a multiplatform release similar to the recent Super Smash Bros. game or The Legend of Zelda: Twilight Princess.