Again I'll have to disagree. How about rather that calling it Halo: 7, call it something else perhaps. And instead of it being like planetside, think of it more as star wars battlefront 2. Large space battles then ground assaults. But imagine those fused together at the same time and being able to transition between the two... in the halo universe of coarse. Now that would be cool. But if not a game itself, possibly a gametype.
Also, there's no such thing as the 'Promethean War '.