Assuming Elites are playable on Halo 5, then I was thinking that they should combine Dominion with Invasion on large maps with at least 16v16, maybe more.
What I mean by the Hybrid is getting the UNSC v Covenant aspect from Invasion and combine that with the Base capturing and vehicle spawning aspects of Dominion.
The reason it should be at least 16v16 is that it would be a good reason to include some more powerful vehicles and weapons, such as the Cobra.
The maps should be large, like something the size of 1v1 Halo Wars maps if they were scaled correctly to FPS.
The Objective could be to gain control of the three bases like in dominion, but the bases would be large and take longer to control. the two teams should spawn in a protected base and are able to spawn vehicles and possibly weapons. the weapons and vehicles available to spawn would gradually get more powerful over time, like in invasion slayer.
there could be multiple ways to take control of a base, such as going inside to hack it, or maybe shooting at it directly with powerful weapons and vehicles, and after doing a certain amount of damage it would open up an outside hacking area.
These are just the basics of my idea, some things would probably be added or changed.