So, I made a landscape, dropped part of it to the floor, and another to the ceiling, then measured. It seems the vertical range limit on a single landscape is about 510 meters. Honestly that seems kind of low to me. If you go that distance all at once then yes, it seems like one hell of a jump, but if your making an open world game of some kind, then .5km in possible height, (assuming all of your landscape layers are zeroed out in Z), is not much to work with.
AFAIK the longest vertical drop on earth is ~[FONT=sans-serif]1,250m, so about 2½ x what landscape supports, and while something like that would make more sense as a mesh just from a detailing standpoint, if you were making a game level that climbed from “sea level” up into the mountain in a “seamless” fashion you’d smack into that 500m limit in short order.
[FONT=sans-serif]Again, I’m not actually “making” something like this, or asking how sane it would be in a gameplay environment. I’m well aware populating massive open worlds is a pain, but this still seems like something that should be doable.