Pikmin 4 is the presumed title of an upcoming installment in the Pikmin series.
Nintendo confirmed in a later statement that the game was in development, but refused to give any further details.  As of July, 2016, the game remains in development; according to Miyamoto, the game has not always been a high priority within Nintendo. It is most likely going to be on the Nintendo Switch.
On June 2017, Miyamoto confirmed that Pikmin 4 is in fact still in development by the Pikmin team, which also means that it is not the same thing as Hey! Pikmin.
There are a few currently know possibilities for the premise and story of Pikmin 4. It could pick up immediately after the end of Pikmin 3, which shows pikmin running to investigate an unknown object that fell from from space and presumably crashed on PNF-404. This scenario is reminiscent of Pikmin's opening, where Olimar crashes on the PNF-404. If the story centered around a stranded explorer, the gameplay would like be similar to a previous game, collecting resources for survival, possibly parts to repair a ship, or food to survive while awaiting rescue. It is also possible that the game could have the player managing multiple objectives, combining all previous games, such as collecting parts to repair a ship while also having to locate food, and maybe collecting some treasure on the side. It is also possible that the object seen in Pikmin 3's credits was not crashing, but was purposely landing on PNF-404, as what happens to it as it lands is obscured by trees, although this seems unlikely, given the object's constant high velocity even when just above the ground, and the amount of smoke and flames coming from it.