Howdy. I've chosen to come out my self-imposed lurker status to throw out an idea I've had ever since ye olde X-Com.
What might that be, you ask? Close Air Support! I'd always liked the idea of having such a feature available, especially since it will give a tertiary use for hangars alongside another style of play.
Now, the very first issue to tackle would be What types of aircraft would support?
There's a bit of variety in how that could be handled. Personally, I believe that helicopters or other rotary-winged vehicles (up to and including hover platforms at a later date) would be better than jets. The reason for this is two-fold: helicopters, although still fuel intensive, are not so expensive as jets to fly. This would be simulated by lower maintenance costs. Secondly, a helicopter would be able to perform several fly-overs at different angles, whereas a jet might be traveling altogether too fast to do anything more meaningful than dropping one piece of ordinance.
So, assuming that helicopters would be chosen as the source of CAS, the next and most important question would be how would it work?
I'm going to be honest and admit that, yes, it could be either a waste of money or an overpowered mess if it isn't implemented right. It can't simply be something that, by paying another $30,000 dollars, you get access to missions where half the aliens are bleeding out on the ground before you even land.
But, with that said, it can't be so weak as to be useless or a waste of money. Perhaps it could be balanced out by a potential destruction of the UFO, negatives to Mission Performance due to blowing a bunch of holes in a civilian area, and so on.
I'd be hesitant to make it a "call-in" ability, since that'd be taking a step towards making it an over-powered sniper rifle, so one would assume the effects would take place before landing. Perhaps a 10% chance that each alien would take a direct hit by either a handful of MG rounds, a rocket, or whatever else you'd have equipped on the helicopter. There'd be a chance for houses, barns, and the ufo itself being either damaged or on fire. Smoke, blast areas reminiscent of rocket and MG fire.. Basically atmospheric effects to show that, yes, a helicopter really was strafing the area before you arrived.
With all that said, I can understand if others either wouldn't want to see this feature in or would have it an entirely different way. I'm almost retiscent myself, having come to love Xenonauts as-is, but I'd thought I would put this out here all the same. You never know if someone's been thinking the same thing!