Just gonna leave this here, reminds me of the Pikko server days with the exception that these guys are showing what is happening in their engine vs a PDF and hype. That said, I'd be surprised if this runs semi smooth, seems like it would wreck client side perhaps. Too bad BE didn't have access to something like this to give us some bigger maps and battles if not open world. I love UE4 but it is definitely weak on the scaling side for MMO like games although I am sure there is work happening to improve it.
It has been done before and successfully over 10 years ago. Which baffles me as to why it can't be done now. http://www.battlegroundeurope.net/
My guess is because the technology is now lost, much like how modern science is unable to provide stores with a power source that's compatible with my old external hard drive. It's like looking for tech from the Dark Age of Technology..
Simulations are one thing, actual life situation is completely different one. I speak that from experience as a game designer. Until they provide an actual life footage of all these players being connected without lags in a seamless world I will not believe it.
That reminds me of the overhyped game trailers. They got unbelieveable graphic and details... but the real ingame version is something different from a short extra rendered video. And like always its made with an special gameengine.. try that with UE4 and we can talk about that putting into EC.