IDEA- Free roam Coop in Halo 5

The idea of firefight/spartan ops returning in Halo 5 would be great, but I feel as if something completely new should be added. My idea would be a free roam mode where you and your friends use your customized spartans to do things such as cruising in a warthog together, running around killing a bunch of covies, or even cooler: Coop missions! This is just a vague idea, but I think it could be crafted into something truly revolutionary. Do you guys think this would work? And what other ideas do you guys have for something new besides spartan ops/firefight?