I know it's a long way away from being even considered implementing with where the project is now (which is really impressive as of its current state, hats off to all involved), how do people feel of at least the philosophy of the addition of vehicles? I think it would be something different and quite cool if done in the right way/on the right maps. Specific examples of sized maps which I believe would be warranted for the inclusion of vehicles are maps like urbannights, where it's a huge city/block that can have as much detail in it as the creator wants and still be seen by ease of access, with drivable vehicles along the road. On the ease of access, it offers players on larger sized maps quicker access to a fight/objective and therefore increasing the flow of the game. And what action movie doesn't have some kind of extreme car chase (law of averages indicate some, but there's no denying they're a huge figure in blowing shit up/killing people movies).
Vehicles to be considered could be along the lines of either luxury vehicles, police cruisers or sports cars - who wants to drive a minivan getting shot at (throw a baby on board on that bitch)?
I know that this is oriented towards a more concentrated version of battle, taking places on roof tops and confined spaces. But I think larger maps, thus facilitating the need for vehicles, would add a new kind of flavour to the game design and possibly drawn in a different kind of audience that is interested in size and overall largeness of a battle/match taking place. Size matters.
I'm not taking into account any coding within the Source engine, as I'm unfamiliar with programming, but obviously supports them (the Buggy in Half-Life 2, etc.)
Just a thought. Again, really nice work.