The ability to move vertically or horizontally without turning the ship is strategically logical, and not to mention, very cool.
For example. Between me an the enemy is an asteroid. While stopping or slowly moving, I could fire my torpedoes or any low arc weapon, use my thrusters to move downwards while using the asteroid as cover and time to recharge my projectile weapons, and fire again as my ship passes the asteroid and the enemy becomes in sight. As you can imagine, this is highly tactical and entertaining.
This type of maneuver is very common in the Star Trek canon (specially the new movie) and in many space games, shows and movies not to mention real life like the F-35 Lightning II.
This was discussed during the open beta and shot down by the devs (if I remember correctly)..
The bottom line then was it's not going to be in the game period.
Nor was it going to be added in the future...
Which really makes no sense to me being STO uses the same (a bit modded) engine that they used for CO which has up and down in it.