In light of removing split-screen from Halo 5: Guardians, 343 Industries' founder and head Bonnie Ross has acknowledged the decision was "incredibly painful for the community" as well as for her and her team. As such, all Halo games moving forward will support split-screen.
In July 2015, just a few months prior to Halo 5's launch, 343's Josh Holmes blogged about why the then incoming intergalactic shooter did not support split-screen co-op play on Halo Waypoint. "The decision to remove split-screen support from Halo 5: Guardians was one of the most difficult ones we’ve ever had to make as a studio," he said. In conversation with GameSpot later that year, Microsoft's Phil Spencer suggested the move was in-line with more players playing online as opposed to within the same room.
But this did not go down well with players, and is something 343 is trying to remedy going forward. Speaking at DICE 2017, Ross suggested the developer has learned from its mistakes and that split-screen play will be reinstated "for any FPS going out" in future.
Moving forward, every @Halo FPS title will have split-screen! Just confirmed by Bonnie Ross (@PlutonForEver) at #DICE2017 #Halo pic.twitter.com/ns28NK579DFebruary 23, 2017
"We've also had a lot of learnings along the way," Ross says above. "When we fell down with multiplayer launch of MCC, or when we didn't put split-screen in with Halo 5, it was incredibly painful for the community and for us. It erodes trust with the community, as the community is a part of our world-building. A lot of learnings from that. I would say, for any FPS going out will have always have split-screen in going forward."
As Spencer made clear at E3 last year, Halo 6 is heading to PC by way of Windows 10. It looks like this will include split-screen support—but I'm guessing we'll learn more between now and this year's E3.