What would this actually do, though? If you could just gun down anyone in the drop zone with helicopter door guns or whatever, all it means is some free kills in the opening of the mission if aliens even spawn near the drop ship, which they don't in Xenonauts 1. I also see it encouraging turtling and AI-luring, as other postsers pointed out. I suppose you could get chances to use it in a wide open map, or if the helicopter happens to be angled right as to give you a lucky sight line down a street or something, but all I see this doing would be taking challenge out of gameplay.
A better implementation would be to allow soldiers to shoot out of the view ports of the helicopter. The soldiers in the helicopter would have heavy cover, but would be able to hit aliens outside just fine.
However, come to think of it, I have been playing with an idea of a special type of mission for when your troop transport gets shot down. If this happens, instead of just losing everyone on board, you start a mission where the helicopter has crashed and is damaged and some of your soldiers will be dead, and most or all of the survivors will be wounded. Aliens then assault you, rather than the other way around, and if you lose all your men, or perhaps if the helicopter is destroyed, you lose the mission. In a defensive mission like this, where you had to spread out your troops to guard the helicopter, I suppose it would be fun to have a kind of "last stand" situation where you have been driven all the way back to the drop ship and you have a heavy gun or two to provide some fire support if manned by Xenonauts.
I'm more concerned with how you can't look out of the windows of the drop ship in many X-Com games, I seem to recall this being the case in Xenonauts, too.
Edit: have to say I dislike the idea of auto-firing weapons. Sounds like a good way to get my own squaddies killed.