I want a game, it's a game with a mix of Planetside 2, GW2's WvW, and ESO's PvP.
Keep it fantasy, vehicles are various mounts, polymorph spells, magical constructs, and siege engines. (Polymorph horse allows you to travel quickly and carry a rider, large golems can serve as slow mobile spawn points and apcs, something like an oiliphant can be a siege breaker loaded with cannons, polymorph wyvern and dragon functions as air vehicles, stuff like that)
Accessing the 'vehicles' require resources like planetside that slowly regen over time and consist of the different types of vehicles (polymorph, mount, construct). And the more basic vehicles have similar versions for multiple resources. For example, polymorph horse allows you to carry a rider, but you yourself can only attack in melee. An actual horse mount only transports you, but you have all your attack options available. A construct horse better protects you from enemy attacks and has more hp, but is a bit slower. A wyvern mount will automatically try to sting in melee range, but is less responsive to control, while polymorph wyvern gives you finer control, and allows a second player as a rider, but the sting must be used manually, stuff like that. It allows for slightly different versions to be used in different situations, and say if you use a horse you have 3 tries to get to your destination quickly before you are forced to walk there.
Playing the game allows you to choose skills from a skill tree, but you can only have 4 skills useable at a time, allowing for newer players to get a full skillset quickly, but giving veteran players a wider range of skills to choose from. Vehicles have their own skillsets. Players can also choose to specialize in a particular kind of vehicle or infantry type, giving them greatly reduced resource cost an extra skillslot when using that particular vehicle or as infantry, and access to a specialist skill, at the cost of one less skill slot as anything else. You can choose to specialize without cost, but you can only change specialty once per day.
Siege engines require a combination of either polymorph or mount points and construct points. When you spawn one you get a siege engine on the back of a wagon, pulled by some large beast of burden (which may be you if you chose to use polymorph resources) you then drive the wagon to where you want to set up the engine and deploy it releasing the animal (or ending the polymorph) and prepping the siege engine for use.
...basically I've been playing too much Planetside 2 while waiting for ESO.