The Reckoning looks to be a timed mode that lets you farm armor to be used in the new Gambit mode. They're making Gambit Prime and the Reckoning go hand-in-hand with each other. Where if you play one you get stuff that helps with the other. When asked what PvE players had to look forward to Comso said Reckoning, the new quest, and the one seasonal event. I'm personally going to try Anthem and the Division 2 when it launches, because an entire season/DLC of Gambit centered activities is not what I want to spend my time on. For those that enjoy it, I'm happy for them, but myself and my friends aren't in that group.