Lag is gonna be a big issue.. In CS, you need a ping of <50 to have a fighting chance, because lag/response is the difference between killing or being killed. In WoW, 300 pings arent so bad, because they make up for the lag with your attacks/cast times. But, you gotta think.. you do only have 256 on a server at a time.. so maybe <100 pings would be possible and still half playable.
It will be interesting to see how they do it. I mean Tribes servers handled a fair few people online at once..
I'd also like to see if they could develop a ranking up system, that may (like in real life) help put you in a position of authority over lower ranks. In the intro of that video, it looks like a chain of command.. so maybe it will work up that way, and certain ranks will be given power over teammates underneath them.
*shrug*