"Better Physics/Simulation accuracy"
What exactly does this cover? The integration of the equations of motion allow you to set your own error tolerance, so I guess this means something else?
I'll take a crack at what it may mean. Well, since you guys over at GA are always trying to figuring out ways to improve the game, to make it better, one way of doing that is tweaking what you already have in place. I guess you can't really get any more accurate then what you have now, so perhaps that's why the question seems superfluous to you. Math can only get so right. Once you have your answer, that's it.
Now, I do think what is hard is keeping that performance and accuracy there when you update the game. I bet its hard to know the unknowns because you're not sure if a new update will break or fix an aspect of the game. I also assume that "Better Physics/Simulation accuracy" could mean further improving speed and performance. When you guys updated to Alpha 16, the speed, fluidity, and performance of US2 seemed to improve dramatically compared to previous updates.
And I've also heard that you guys are working on getting the game to run off the GPU. That sound awesome because it should make performance skyrocket on capable hardware. My GTX 980 eagerly awaits that day.