They need to drop this lofty goal of having 200 players on screen...
The recent King of MMO's, World of Warcraft, doesn't even try to be that audacious. In the pvp, the most they've tried to do a 40 vs 40 battleground where those 80 players are spread out across the entire zone. Still, I generally think that being realistic about graphics is a key to an MMO's success - there are many different players with many different rigs, and the more inclusive you are, the better usually. I am worried, however, that if people pick up Elder Scrolls Online expecting 'Skyrim Online', and then find that they've gotten 'Cartoonworld Skyrim: Online' then that will cause some problems...
I'm sorry but WoW PvP is a joke. It's like CoD; just rinse and repeat in an instance or arena. And Blizzard couldn't balance their low number of classes if their life depended on it. WoW is PvE driven. PvP was always an afterthought in WoW.
DAoC started years before WoW and you had multitudes of people fighting each other while siege weapons destroyed a massive medieval style keep. There would be 50+ ppl inside the keep defending while another 50+ assaulted and rammed down the keep gate; or punctured a hole in the wall. Then you'd have a massive rush as 100+ ppl beat the piss out of one another inside the keep and inner tower. Swords clashed, Thor hammers reigned down in an aoe, arcane spells blasted enemies, stealthers popped on casters and one shotted them, achers slew healers from the walks, guild banners shown on every other person character, healers avoided enemies and healed like no ones business, CCers tried to land a 50 sec mezz on groups of people, boiling oil poured down in the attackers. And then in the heat of this epic battle, THE THIRD REALM WOULD SHOW UP WITH THEIR 50+ PPL. They'd flank the two sides and suddenly you have complete chaos as 150 ppl are fighting and dying all around the keep.
And this doesn't even cover open area battles on your way to a keep or tower.
All of this epicness was happening back in 2001 and it rarely lagged. For the most part, it was magical. We can only hope ESO will come near that.
Also DAoC had like 21 races and 47 classes!!!