Personally, I think I'd rather the abstract tank crew. Numerous characters aren't going to have anything to do with a tank, and might only be near one that was a Chimera they rode in. Having a character with the Drive skill, to do so, would be nice, and if you need to operate the lasgun-mounts, or such, okay, but if your character will be a tank, such as a Leman Russ, then I think I'd rather that each was a tank, and you just run it, and the NPCs, like a one-man crew tank. Then, your characters who aren't tanky, say your stealth-based sniper team, or your Ogryn Assault Squad, can still do their thing, while you bring down the sky with a Leman Russ's battle cannon. Having all your party in a tank, with one doing the occasional Drive test, two shooting guns, and one barking orders at them just isn't as fun to me, when your party could be more efficient spreading out, each doing their specialty, and feeling more like they are the victorious army, rather than one tank in it, that happened to blow a tread. Also, if my first wish is granted, and they balance out weapons, so that they can ding/boom vehicles, without killing infantry just for watching you reload, some tanks might not be the best place to stow the whole party. A melta-bomb that works on the side of your Hellhound might spell doom for you all, as the blast fills the tank with death, and the survivors, if any, then watch as the promethium stores detonate, sending you physically rocketing to the Emperor's bossum.
Anyway, that's my two bits; make one character a "tank operator", who pilots, barks, and shoots, and leave the rest to slog it on foot, where their specialties can still apply. Otherwise it's kind of like Star Wars RPG, to me. In that, I will either build an Ace Pilot, and strike fear in the Imperial Navy with my invincible starfighter, OR I build a powerful Jedi, and strike fear into the Imperial ground troops with my bringing justice back to the Republic. The two don't particularly mix well, and characters who aren't dedicated pilots, called upon to act like they are, often fail, while fighter aces on foot suck. It's good to know which style you will be in, first, and build accordingly. Hopefully, this game will understand that, and allow a character to operate a tank, more or less as an extension of themselves, sort of how a Dreadnought works (yes, I am well aware that a great deal more goes into making a Dreadnought work, but it's the principle of the thing), and let the other players do their thing, whether that's drive their own tanks, scout ahead and paint strike spots for distant Basilisks, or shore up behind a wall, and pour heavy fire into enemy infantry, while someone is coordinating all of this with a beautiful string of orders that show why the Guard has been enough, over the millennia, to hold onto the Imperium, even when the Space Marines are too busy fighting the handful of epic fights that the Guard couldn't handle.