Epic Games has made several improvements to Unreal Engine 4 to accommodate the scale battle royale games require.
A big reason for creating these is of course the company's own Fortnite, which recently launched its Battle Royale mode. When Epic started working on the mode, it identified many parts of the engine that could get improved. The updates cover server performance, object rendering, and more.
To start with, dedicated servers should now better support the large number of players as a result of streamlining in the some of the processes a server performs for every player. The change log includes a lot of technical jargon, but the idea is to have consistent experience for all players at 20hz.
30hz and 60hz servers also saw improvements, with the input lag being reduced thanks to updates to thread synchronization.
Battlegrounds-like games tend to have massive maps, and Epic has worked on its level of detail system to allow for longer view distances without sacrificing performance. This is particularly important on consoles, where memory is more limited than PC.
Some of the changes mentioned will be available in version 4.18 on Unreal Engine 4, which ships this month, while others will make it out with version 4.19. Hopefully PlayerUnknown's Battlegrounds will be able to make use of these updates.