[Suggestion] The ability to make a Gravity Elevator/Train at Advanced Science Skill Tree Tier
The idea came to me when I first discovered the skyhole bug in the terrain a few weeks back and I was thinking instead of patching that bug completely you could make it into a feature (It's not a bug, it's a feature waiting to be discovered) by allowing you to make a Gravity Elevator/Train once you reach the Advanced Science skill tree :)
A gravity train is a theoretical means of transportation intended to go between two points on the surface of a sphere, following a straight tunnel that goes directly from one point to the other through the interior of the sphere.
In a large body such as a planet, this train could be left to accelerate using just the force of gravity, since, during the first half of the trip (from the point of departure until the middle), the downward pull towards the center of gravity would pull it towards the destination. During the second half of the trip, the acceleration would be in the opposite direction relative to the trajectory, but (ignoring the effects of friction) the speed acquired before would be enough to cancel this deceleration exactly (so that the train would reach its destination with speed equal to zero).