[citation][nom]Jea3cd[/nom]WWIIOL or Battlefield Europe already has done this. The Map is like 1/4 scale. So you could jump into a plane in England, and fly all across Europe, land in Brussels, get into dog fight over Liege, or get into a tank in Namur and drive to Ramet. You could line up thousands of people on the road, and drive a Betty down the road and salute to all the troops as you drive by. Great game.[/citation]
Like said above, WW2Online did have a single server with an FPS style with way over 1000 at any one time, but any one client could only see roughly 128 players at any one time. (Remember they built this game with 56K in mind when it started) so you were able to limit it down to 32 or even 16 I believe, but then you wondered why you were dead when you didn't see any PZ in the distance. :/
Overall they have a great system still and while it is old vs todays games, I still gravitate back every now and then because it really is so good.
WW2Online, and EVE are my 2 fave MMO's. TOR is a good little break from the complex style of those two, but nowhere near a replacement.
I can see the 1000 Player FPS feature becoming commonplace for many MMO's as long as the game map and setting can handle and really benefit from such a large number of player. I could see the future game Dust 514 being a big candidate for something like this.