My dream is still that Halo Infinite is an "open world" with both open-world levels and discrete, linear ones. And the "open world" in this case is just... Zeta Halo.
You can call the pelican flown by Beard Guy, and have him seamlessly pick up and drop you off all along the ring. Different biomes, different wildlife, forests, lakes - all of it. You could maybe have small transitional sections to hide the loads between areas if necessary, kinda like Destiny does. In the first teaser trailer, we saw lakes, and grasslands, and desert so... maybe?
A personal warthog you can store armaments and stuff on would be cool too. Maybe Beard Guy can even be called to drop it off with the Pelican.
Give MC a variety of tools like the grapple hook to navigate tougher terrain, and make the ring worth exploring aside from missions. Zeta Halo is a pretty lore-rich setting, so there's tons of things you could put there.
Of course, then I remember this game comes out on Xbox One too, and my dreams start to dissolve a little.