Since we are in Twisted Metal dream list mode, here are some things I'd like to see
-Cockpit view.
Would really add to the immersion and gameplay. I think a lot of people would like to know what the insides of their favorite Twisted Metal cars look like.
-Extensive damage modeling / physics
In past TM games, our vehicles show visible wear and tear as they get hurt, and then they explode when "dead." I think there needs to be a much more dynamic fatalities for the cars. It's time we live up to the name "Twisted Metal" and actually twist the metal in all kinds of wicked ways. Look at some horrific car crashes and go from there. Do I want to see Sweet Tooth's truck get split in half from Mr. Grimm's special? Yes I do. Do I want to see Mr. Grimm get ejected off his bike and crash into Sweet Tooth's windshield? Absolutely. Think MotorStorm but with more death.
-Car / mounted weapon customization
Since this new twisted metal would undoubtedly focus on online play, there will be many people playing the same vehicles. Beyond letting the players alter their cars appearance a bit, various user customizations can have different bonuses and trade-offs. For instance, you could heavily fortify a vehicle with plated armor, but you'll also move slower. And plated armor may be effective at stopping missiles and gunfire, but is very vulnerable to blunt physical attacks like Ricochet's, or fire based attacks like Napalm. Of course, everything needs to be carefully balanced and counter-balanced. Still, there's nothing wrong with letting players specialize their vehicles beyond the standard stock vehicle.
-New close quarters combat gameplay
So an often effective strategy in past Twisted Metal games no matter what type of vehicle you are is to ram your opponent, hold down your machine gun fire and blast away with whatever other weaponry you have on you. I think this should obviously cause some collateral damage, firing at vehicles point-blank should hurt you almost as much as it will hurt them. So this should only present itself as a viable strategy in certain cases or for the very largest of vehicles. Of course bigger vehicles are aggressors and are meant to be up close and personal, but they should have the tools to do so in their own way (latch on with chains or hooks, tractor beams, magnets, lock your prey's tires, etc.) Look at Dead Rising and how they're utilizing various weaponry (dual-chainsaw motorbike) there's no reason this kind of stuff can't be incorporated into Twisted Metal to give the close combat more depth.
-Crazy environmental hazards and destructibility like past Twisted Metal games
I know this sounds simple, but sometimes simple things like this get overlooked. Blowing up the Eiffel Tower in Twisted Metal 2? Wicked. Glacier level collapsing over time and taking out opponents with it? Awesome.
Basically, that's my dream twisted metal. I don't know how I'd feel if it was open world like Burnout. I think I'd rather prefer something more "closed but open" in design like Warhawk. And I know a lot of the Eat, Sleep, Play developers worked on that game, and worked at Incognito, so I know they'll pull through regardless.