Right now, they are only talking about a tech demo. But this here could become highly relevant in a short time period:
As far as i know, Planetside 2 is still the reigning king of any truely fast, realtime PVP multiplayer. But its tech is 6 years old and was never fully stable. 10000 players sounds like a horrible lagfest no matter what, unless you do the classic “cheat” of splitting them up to not actually be in the same fight/place at the same time, or have some slomo gameplay.
But still, scalability for truely large realtime player interactions is a super fascinating prospect. There are so many types of games that so far do not really have the option to go massively multiplayer.