You can alter the terrain of asteroids by shooting at them with the spaceship's lasers and I'm guessing every landscape object is treated the same in the engine, so landscape destruction probably is already in. Problem is there's likely no physics attached to it, so you'd be voxel mining like Minecraft. When the cube chunks are taken out the landscape is probably going to look a bit off. And it's unlikely the game will track many changes locally, and it definitely won't track them online for more than a few players, and then only during a single session.
In other words, there's a decent chance you can dig a hole, but when you leave the planet and come back the hole will be gone. And if you dig too many holes in the same area, the first hole you dug will start to fill in again.
Sean Murray does refer to the terrain being made out of voxels, and you can tell when he wanders around in the tech demo video. There's lots of smoothing and blending to make it look good, but it seems to still need some work. Stuff like trees, grass, and stalactites are probably just objects that attached to the voxels, like a texture, so whatever voxel physics exist probably won't apply to them.
this a game i would hold dear to my heart, if it fails to deliver i may actually lose faith in game design as whole. since i would be devastated
What do you expect it to deliver? I've seen an incredible variety of expectations, both positive and negative, many of which are highly unlikely.