here is my take on all of this.
1. Small arms fire are not going to immobilize your transport....period. No german halftrack or russian universal carrier can have it's engine or tracks taken out just from a couple smgs or riflemen shooting the back of it. Mgs can't even disable a transport in ROOST unless they wasted belts of ammo and the transport is stationary so that every shot hits. As for the people inside the transport getting shot out, theis can only happen if it's from the front shooting the driver out of the hatch (which would not be the case in this situation) or an mg on the german halftrack getting shot out from the back. chances are, the shooter is not going to hit the mger. heck, chances are there isn't even a player in the mg position to begin with. So, in all reality, the results of what the OP described simply in the current game do not happen. maybe a rare case of an mg getting shot out, but still highly unlikely.
2. players should not be forced to "communicate" to a driver to stop a transport as it leaves the spawn to get them to wait. This issue is partly due to the whole spawning system in general which hopefully is improved for HOS. If you are the only player that spawns and you hop in the transport, wait about 30 seconds. chances are another couple of playerswill spawn and you then you can drive off. imo, no transport should even be allowed to leave spawn unless 50% of it's capacity is filled, i.e. halftrack seats idk 8, you need 4 in the vehicle for it to exit. (of course this would be designed more for large scale pub play.)
3. Some players do not have a mic. Some (probably most) players prefer to not take the time to toggle up their voice commands or start up a text team chat just to get the attention of the driver, but instead choose to shoot a couple rounds into the back of the transport to immediately get the attention of the driver that somebody is behind them and needs a ride. As no real damage is done to the vehicle, this is actually a really effective and time saving way to accomplish the task.
4. is the "tat-tat-tat" on the back of the vehicle annoying? if it's really that annoying that it completely ruins your game, then you've got some issues. of all the possible things that could ruin gameplay or immersion, to pick this out is a bit absurd.
If someone requests pickup, I stop and I wait for them no problem..... but any idiot who shoots at my vehicle is just being left behind out of spite.... if they can't communicate properly, then that's not my problem and I have no interest waiting around for them to shoot me dead due to their foolish antics.
that "idiot" IS requesting pickup by getting your attention. as i already explained, that "idiot" is actually SMARTER to fire two quick, completely harmless shots into the back of the transport than to take 5-10 seconds pulling up his voice command menu, or typing into team chat. those 5-10 seconds could be the difference between getting 4 troops into a capzone to stop a cap and those troops being late by 5 seconds and the team losing the zone. they are communicating, regardless of what YOU definition is, "properly" and it is YOUR problem if you do as you say and "leave them out of spite". you essentially chose to be a douchebag because you thought somebody else was being a douchebag (even though he wasn't).......i'm sure you've heard the common phrase, "two wrongs don't make a right"
of course it's all a different matter IF for example you are the mg in the halftrack and they shoot you out of the top. NOW the issue there is that duh, this situation should only really ever happen while the vehicle is in the spawn area, meaning, the zone should be spawn protected. so even if you were the mg and the guy actually hit you, it wouldn't matter since you couldn't take any damage. if the vehicle can't take any vital damage, and the players inside the vehicle can't take any damage, then what's the negative result of this happening?
this topic really doesn't seem like a suggestion for improving some aspect of the game because it's not fixing anything that is broken. it just seems like a rant about what some consider to be "annoying".