Time-consuming as it may be, option number three doesn't provide any loopholes to exploit. If you're stupid enough to bail on your tank at the first sign of danger, you're sure to condemn yourself to death when your avatar tries to get out of the tank while it's being showered by machine-gun fire in the middle of a raging battle.
I just don't see how people can argue "spawn with tank, die with tank" as a means of reinforcing realism - there are plenty of opportunities to clown around like a dick playing as an infantry-man; run around firing off an entire magazine full-auto into the air, crouch-spam and pretending to hump corpses, bayonetting into thin air. Does that mean that we need to take precautions to prevent this from happening? No automatic firing permitted when sights are inclined more than 45 degrees? No crouching within a 3 meter radius of a corpse? No! Idiots will be around, it's a fact.
But like I said, if an idiot decides to bail in the middle of combat, he'll get riddled with bullets before he can escape, should option three become implemented. It's a problem that solves itself, and doesn't affect the individual freedom of players. Players shouldn't suffer from the refusal of certain people to stick with their teammates.
Arbitrarily locking people into a damaged and immobilized tank when the front just moved forward a click or two probably gives birth to more frustration that the original ROOST-system ever did.
More-over, crewmen were only armed with sidearms, and only in rare instances, were given one submachine per tank. Hardly a serious threat.
If locking the tanks are a temporary solution to put the game out earlier, I fully understand that. But if it's a permanent solution for gameplay purposes, I find it contradicting and dumb. (I'm not dissing Tripwire, I'm merely stating my opinion to this particular question)