I’ve been researching this issue myself instead of working this morning. This is all I have gleaned, I could be wrong though so take it with a grain of salt. Single player is in better shape than multi, but see this link for a discussion of Unreal tech for a server side solution to larger worlds. Basically it’s going to take some work on your end. Also here.
TLDR; A) World Browser at this point won’t let you do a world that wraps back around it seems. B) Changing streaming distance at runtime would be cool, hopefully they’ll expose it as they develop the world browser C) size and scale will be a function of performance, and really, for most computers, having 8k of heighmap being displayed at once (no matter how you stretch/scale it) is quite a lot of data. I’m in the process of running some tests, but I’m starting off with terrain scale 100 and a max view distance for of about 12 kilometers. I’m hoping that beyond that a little horizon fog, proper terrain occlusion, and some luck will keep me from seeing the edge of the earth.
One thing, though this depends on your needs: terrains really don’t need to be that high-res, with a normal map baked from a high poly version of your terrain over the whole terrain tile and some other shader tricks (global color map with AO Cavity and Edge maps along with a tiling noise normal) you can really get some good looking stuff. I’ve actually ran into the opposite problem when using world machine, too high resolution and the terrain becomes unplayable because of all the erosion channels and funky stuff going on. More often than not I find myself smoothing the terrain down in world machine after baking the high resolution terrain for maps so that it’s not a PITA to traverse. Most terrains are actually pretty smooth in part so you don’t get stuck, and you don’t need a lot of resolution for that. Consider using static meshes in the places you need that little bit of extra detail (sharp cliffs/etc).
and vote for the large world coordinate system on the roadmap.
Just my .50