Guys they announced Halo 5 is going to be locally single-player only. Sign this petition to change that here: https://www.change.org/p/microsoft-343-industies-bonnie-ross-kiki-wolfkill-microsoft-studios-add-split-screen-co-op . Be a part of the people that keep Halo the way it's supposed to be!
It wont happen. The game was optimized to run without splitscreen, so even if they could add it to the game with an update, it would make the game run like ass.