Just too lazy to test case it myself.
I wonder what made the devs choose world_max to be 20 KM? while its known to get erroneous after 8KM at 1cm per unit resolution.
can you still get reasonable accuracy near worldmax or is it all jitter?
Also UDK was limited to like 8Km I guess , what changed in UE4?
You know, you might be too lazy to test case… but you shouldnt be too lazy to google 
It’s possible to create “infinite” seamless worlds. UE4 supports world origin rebasing. At certain moments (when camera position is far enough from current world origin) engine will shift world origin position to current camera position. Basically this operation subtracts a specific position offset value from all active actors in the world.
To make it work you will need to compose your world from a smaller streaming levels (tiles). Tiles should be loaded based on distance from the current camera. Each tile should have a “world position” which tells engine where that tile should be positioned in the world. While player travels trough world - engine compares tiles “world position” to a camera position and decides whether tile should be streamed in or streamed out.
ah yeah , unfortunately that’s not feasible with multiplayer yet.