To be honest I could see it be more like what they did with infinite. Basically have it be a decoupling of Halo's multiplayer from the campaign permanently. If you want Halo multiplayer you play that game and if you want campaign Halo you buy the Halo campaigns.
It could work if done right too. You would no longer have the splitting of the player base up between games because it would just be a constantly updating multiplayer that introduces new weapons, modes, vehicles, etc over the years. Now will it be done right? I have zero faith in that.