It should be high priority, though. It really destroys a lot of the game's immersion.
"Immersion" is not a priority.
Priorities are (or at least should be):
1) Game is stable. Whatever you do doesn't cause the entire game to crash, it doesn't cause unexpected reactions, or cause the game to behave in unpredictable ways.
2) Game is mechanically functional. When you put thrusters on your ship, it lets you move forwards. If you link two weapons together correctly, you get the new weapon type to activate.
3) Game is playable. Assuming what you've done doesn't crash the game, and it basically works as intended, next priority is making sure the player can interact with this new whatever in an intuitive and easy to manipulate way. Example, if they added attitude thrusters to make turning large ships easier, they need to be something you can just drop in the ship and have them work, not be something you have to core jump to each thruster individually in order to make it fire. Such a system might not crash the game and technically works as intended, but is so clunky as to be unplayable.
4) Immersion. Adding cool textures, sound effects, etc.
Immersion is literally the *LAST* thing on the priority list. Make the game stable, make the game functional, make the game playable. Those are the priorities.