Someone posted a new image in our
subreddit if anyone doesn't have a CHC membership
There are very little details on that but we can make a good assumption on both
1. Their last game scream ride, had a spline based coaster editor. You would use the joystick to alter the coaster in any degree.
2. There are confirmed elevated walkways, which we can assume it's mainly used for hills.
3. They built rct3 which had a very, very, extensive land editor. Which includes what you mentioned.
4. Sandbox mode is confirmed. Sandbox usually means there are no limits, creating a sandbox mode also means the developers have gone the extra mile to make more modifications possible. You can't think sandbox without thinking of modifying the terrain.
5. There are confirmed underground coasters and tunnels. They will build coasters to go underground, why not through mountains?
So although there isn't a answer yet, we can say both are pretty likely.