you know what would also be nice? just once in a while, a UFO should crash into a house. or a hill, for that matter. this could be done by hand-crafting a crashed UFO with a structure around it, but I think the engine should also be able to do that automatically (at least with circular UFOs): create the battlescape, generate a completely overpowered explosion limited to the radius of the UFO, insert the UFO into the cleared space.
Actually, the engine sort of works like this already: with imperfect maps, you can get your landing craft occupying the same position as a UFO, which results in part of the UFO obliterated and your Avenger standing there, among the rubble. (Yes Luke, I remember
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speaking of that, would it be possible for the engine to place a UFO somewhere else but in the middle of the battlescape terrain tile? I am aware that his might cause all kinds of problems, including blocked doors etc, but if it's implemented with safeguards, it could even be fun... think of UFO crashes where the doors are blocked, but you can climb on top of the UFO via the hill it crashed into and enter through the hole in the roof... or the doors are blocked by debris that you have to blast away first... and if you don't have the necessary explosives, you'll have to leave and come back later (that would need to be an option, of course... semi-permanent crash sites... hmmm...)
Indeed, actually placing a UFO inside a pregenerated terrain isn't quite possible now. As you wrote, the UFO has its own map block, which is empty except for the UFO itself. Changing it would be possible with some coding I guess, but it would require dealing with issues such as routes, which exist in and around the UFO but would often be blocked if the UFO fell on a house. And if the entrance would be blocked by walls or even worse, by densely packed earth if the UFO crashes into a hill, then much hilarity ensues.
Creating the destruction path going from the UFO in a random direction would sort of simulate this, without causing all these problems... Though it's obviously less immersive.
I'd love you see your version implemented some time in the future, but it's not very realistic right now; mine is.