“It’s actually very close to completion,” Miyamoto told Eurogamer during a July interview. “Pikmin teams are always working on the next one.”
Nintendo also confirmed the news to Eurogamer in a separate statement:
“We can confirm that Pikmin 4 is in development but that is all we can confirm at present.”
Neither Nintendo or Miyamoto stated which platform Pikmin 4 is in development for, but Eurogamer suggests that given it’s near completion, it will launch for Wii U.