You seem to have forgotten some basic issues with that idea.
You're in space, yes, but even if you were as far away from the earth as the moon, you still have gravity from the earth to pull you if you had stopped moving. Hence why the ISS constantly needs people to visit it, they need more fuel to not fall back into orbit.
Second, technical issues with the idea in terms of coding difficulty. It's one thing to have no gravity, it's quite another to have full range of motion. So even if you could have no gravity, you'd still have a up and down because the game doesn't work without it.
Last, no gravity means you need to get around either with vectored thrust(aka a good jetpack) or by moving from wall to wall. Or of course, always straight towards the largest gravity field affecting you. And if you used a jetpack you would keep moving long after you let off the fuel because no gravity means nothing to reduce your thrust aside from more thrust. And you always spend more fuel slowing down then speeding up because slowing down means you're fighting against your thrust. That thrust is thus your new gravity and you have to fight hard to get out of it's grasp. Long story short, ion engines are much safer when you exit earth's gravitation field because you don't have as much thrust to screw up with.
Actually, since there is no friction in space due to it being a near-vacuum, the ISS does not, in fact, need more fuel to stay in orbit. The main reason people are always coming and going is that the human body can't handle being in zero G for very long.