Mapping a crash-map would be fairly easy. The damaged dropship would be the only new asset requirement, everything else is already available. Drop points on the map are determined entirely by the map maker, so merely set human drop points around the downed dropship, and everything else can be done just as any other map. Hell, you could have an alien ship landed nearby, with alien drop points, if you want. For random maps, I can't see why this would be a problem, either. Just replace the landed dropship tile with a crashed dropship tile, and the crashed alien ship tile with an intact tile. Pre-injuring the soldiers may take some work, but for now that feature is not necessary.
Now, the other aspects to these mechanics need fleshing out. Alien craft behavior after shooting down a dropship, for one. Does the victorious alien immediately land and attempt to engage, does it torch the ship and retreat, or does it patrol while awaiting a larger troop transport to fly in to engage the crew? What options does the player have? Can he order his troops to flee, decreasing the chance that they are engaged on the ground by a superior transported force? Can they stay nearby to the crash to defend it in the hopes of quick rescue/salvage? Can the ship be scuttled, to deny the aliens PHALANX intelligence?