At tonight's Nintendo Direct, Nintendo announced that Splatoon 2 would be getting another free content update in addition to a paid DLC expansion. The game's version 3.0 update, which will be available in late April, will add a new "Rank X" to the game, which will be higher than the current max rank (S+). The update will also include three new stages (Piranha Pit, Camp Triggerfish, and Wahoo World), as well as over 100 new gear pieces. Additionally, players can now meet Callie in Octo Valley after meeting certain undisclosed conditions.
Source: Nintendo Direct