[cma]

Mostly to do with floating point precision, the devs of Star Citizen ran into the same issue with Cry Engine when they tried to make things space-scale, and ended up initially stuck with small battle-arena maps. UE4 can re-origin things for a single player moving through a large world to maintain physics precision, etc. but it doesn't currently work with multiple people and their server model.

[outworlder]

So, basically what Kerbal Space Program does. Which also doesn't work well with multiple people.