Heres a few ideas i have…
Heretic Banshee
Fires explosive plasma rounds but to keep it balanced it cannot use the fuel rod (sort of how the Banshee worked in Halo 2 multiplayer and since the Heretic Banshee is only ever in Halo 2, it kinda works lol)
Troop Warthog
Scout Warthog you say? Most pointless vehicle ever! Why not make one better, like the Troop Hog from Halo 3. Can carry 3 additional Spartans (so driver and 4 passangers). Also it will have stronger armour as that thing will scream “LAZER ME TO DEATH” if it was full.
Spectre
I’ve been wanting this vehicle back since Halo 2. It was such an awesome vehicle and it seems like its just faded into history, WHY!? Can work just as it did in Halo 2 (ofc it will work like the Ghost and Banshee with limited boost before needing to recharge). If possible still have the reflective plasma rounds, you know, when you shoot something, regardless of what it is, the rounds still bounce off it, just to keep that classic touch.
Brute Chopper
While cannon wise it would make no sence for anything Brute related to even be in Halo 5 at the moment, the multiplayer is simulated, meaning anything from any point in time can be “spawned in”. So, why not the Brute Chopper? Can pretty much just work how it did in Halo 3, possibly give it abit more armour.
Mini Elephant/Mammoth
Ok, this one will be the most unlikley to happen, but if it did it would be amazing. Now this vehicle is, well, a smaller version of the Elephant/Mammoth. Why smaller versions? Well, for it to work in Warzone it would need to be a decent size (i cannot see the Halo 3 Elephant or even the Mammoth getting around March on Stormbreak). Now heres the catch, its well armoured, more armoured then a tank, has no turrets on it what so ever (to give it some form of balance) BUT, while one is out in the match, when you’re choosing a base to spawn, you can choose this vehicle aswell. Its giving you that advantage of being able to spawn pretty much where ever you want while being at the risk of getting spawned killed. It will also create some interesting tactics in terms of where to park that bad boy. One final thing, there can only ever be ONE for each team out at once (it is grayed out regardless of req level for everyone else till the current one is destroyed).
I have tons of other ideas but i will be here all week at this rate!