This is what I was thinking as well. Rather than an equivalent, just make an upgraded Elephant. I'd actually say something similar to the design the OP posted, but how it shows the legs fold up (because of the treads on the feet), just make the folded up position it's permanent position. Don't make it a crawler, make it a larger version of the Elephant. I have some ideas on how to make it work, and still be realistically doable in Halo 4:
1.) A main gun. Perhaps similar to the Rocket Hog's from Reach, but with full powered rockets rather than the weakened ones the Hog has, a larger salvo (around 16), and a much longer reload time. Also, this would be on the top of the vehicle so it can have a 360 degree view radius. This leads me to my next idea;
2.) A control room. A small, yet decent size room for holding out, controlling the vehicle, and operating the main gun. Think along the lines of the Scarab interior from Halo 2.
3.) A vehicle bay. A small room located in the back of the ship, about 4 units wide. What I mean by this is: wide enough to hold 4 small vehicles (Mongoose, possible Motorcycle?), *OR* 2 medium vehicles (Warthog, Forklift, Civilian car), *OR* 1 large vehicle (Scorpion).
4.) A landing pad. A pad on the top for a Falcon or Hornet to land on. This will have to be put somewhere out of the way of the main gun so that it doesn't block the line of fire, my idea is a circular hole cut in the top of the roof and a small room inside the Buffalo you would land in, with a reamp that leads up to the roof.
5.) Turret "slots". I had an idea for what I like to call turret slots. These are circular rings on 3 places of the vehicle (two on the front of the roof's left and right sides, and 1 on the back above the vehicle bay). These rings are where the turrets would go (Machine gun, Gauss, or Rocket), and the ones of your choosing could be placed in forge. If the vehicle was in campaign, the turrets would be pre-decided, most likely machine guns on the front 2, and a gauss on the back.
I think with these qualities a vehicle such as this would actually work pretty well in multiplayer, so long as they're used on a fitting variant such as Invasion, or possibly BTB. I also think they would make for a kick-ass Campaign segment. Now, even if 343 doesn't put them in Multiplayer, it would still be nice to see them in Forge, so the players can experiment with them, and craft a variant where they would work. Hell, if they would've left the Elephant in Reach's forge there's not a doubt in my mind we'd have some pretty awesome Elephant-oriented Invasion maps by now. Now, think about the vehicle I just described, and imagine what the community could do with it...
