I think it's really unrealistic that objects can travel faster than the speed of light or even the speed of light. Also it'd be nice if you could see length contraction of objects as they get closer to the speed of light. Another nice feature that i think should be added is instead of having one tab that says mass, you can see the rest mass and relativistic mass of that object. I think time dilation though wouldn't really work in us2 imo though.