My friend once told some pretty shitty lies (and of course, I had allowed him to continue spouting his nonsense) about how he once played an alpha of StarCraft 2 WAY before it was announced (like, 1999-2001 time was when he claimed he had played it). It was either that, or he was just telling me ideas about what I could do for a StarCraft mod. I think it was the former...
Neither really matters.
What's important was that he talked about air units being able to shift elevations. For example, a Wraith had an "Ascend" and "Descend" button in its button set. And he said there would be 3 elevations or something. He went on to talk about how these different elevations affected combat and speed and otherwise.
So, for the time until now, I've always been rolling around this idea in my head, trying to find ways I could implement this.
Here are the methods I've come up with to simulate elevations.
-From the Starport (or whatever unit builder), you have menus for a unit-type, which when clicked on, is replaced by a button set that presents options for different elevations that unit can fly at.
Starport -> Unit type -> Unit's elevation
-Morphing. Simple. Perhaps an elevation button menu that when clicked on, presents options for which elevation you want. Click an elevation, and your unit morphs to that (it actually doesn't morph of course; it would only look like it's rising into the air).
Wraith -> Elevation menu -> Unit's elevation
-Siege mode. Probably impossible, except for one pair of unit IDs, plus Edmund Duke's IDs. Should be obvious how this would run its course.
So, there. I believe that the first and second methods shall work best. Third will be retarded. Second might be impossible except for a sole few units, unless it's possible to make any unit morph.
As an afternote, I have considered Terran structures for their Lift Off and Land features, but I hardly thought it was worth mentioning considering how hard it would be to implement. Or not. I dunno, that's something to think about though.