I'm not sure how old this discussion is, but the idea is interesting and I'd like to add my two cents.
I'd agree that allowing base defenses to shoot down enemy ships would be too much of a game-changing ability (and it sounds like that idea was shot down, so to speak, so it's a moot point).
However, someone suggested an ability to use base defenses to target and destroy craft which have already been grounded (provided they're in range, I assume). This idea is appealing to me for the simple reason that, as pointed out earlier, the end game of X-Com gets to be very tedious at times. Typically I'll be shooting down a UFO every few minutes - if not more - which then necessitates a trip to the crash site for a ground combat.
Bombing the crash site isn't the only way around that tedium, obviously, and I admit I haven't been able to read all of the information about the game. Perhaps this has already been addressed in the form of an autoresolve for ground combat, or some other method - in which case, feel free to disregard! But anything you can put in the game to help alleviate the constant micromanagement of ground combat (which is fun, but rapidly gets tiring when you'd rather be researching) would be helpful.
