Even taking into account that you could build a ship like that and have a sector size large enough to hold it, ramming it into a planet would probably kill the game on any known server (assuming you would be even be able to approach a planet in a ship that big, and not kill the server while at it, due to planets being already laggy and prone to crashing servers even on their own).
A ship that size would probably have serious problems even being loaded correctly. Due to how entity rendering works in the game, any entity measuring more than 8km in any direction from the core usually ends up corrupted. Even if you put the core smack in the middle of the ship, the sheer size of the entity could cause a lot of lag and other weird things to happen.
Also, you'd probably have a hard time trying to figure out how to get something like that powered and moving in the first place. Even conventional titans (about 1/10th of the proposed size) have enough problems with having enough thrust to move and turn at an acceptable rate, at the current thrust ratios.
