Sadly 2 years after this initial post, still no implementation or documentation, no MultipeerConnectivity.
Even though location based games gain attraction (Pokemon go, Minecraft Earth and more) and there is so much potential for innovation, especially when using an innovative engine like Unreal.
The UE4’s source code has a line about MultiPeer Connectivity (reference in source code here: https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Plugins/Online/IOS/OnlineSubsystemIOS/Source/OnlineSubsystemIOS.Build.cs [access to github required] ). So at some point implementation was planed?
Requests on answerhub, forum and discord server are never answered.
Some devs recommend implementing it ourselves, not considering that UE4 (rightfully so) nowadays has a bigger user-base of indies, artists, designers, not only the classic gaming studio with specialized programmers.
So this feature is in limbo and projects that need MultipeerConnectivity have no planning certainty
without a capable programmer in Swift/Objective-C and C++ in the team.