The way I currently simulate world wrap is to have 3 maps, 1 main and 2 shadows. The player generally stays on the main map, but the other 2 exist to emulate that seamless map transition of a globe. When you reach a certain point in the map you are teleported to the other side so you can continually scroll east or west, and that teleport is almost seamless aside from an almost negligible motion blur which I understand can be removed in post process. When you interact with the shadow maps it changes things on the main map. Without streaming though I am rendering 3 times as many meshes as I need to, which isn’t too bad for my setup but obviously not preferred. Mostly this is just a temporary solution, which like you I would like to upgrade with streaming.
Rama did create a node that lets you spawn actors into streamed sub-levels. Could be useful to you depending on how your level is set up. Spawning tens of thousands of instanced meshes can be a surprisingly fast operation.
Hoping the devs can give us more blueprint control over the whole streaming process in 4.6 though. Would help out quite a bit and should only take a handful of new nodes to accomplish.