I dont think pvp server is need, there are various way to add in pvp:

1. System allow player to flag themself as pvp or pve with 24h CD to prevent abuse, mean the player can turn on pvp and pvp with other ppl in the current map w/o effect pve player and will not ruin anyone immersion.

2. Add in pvp map with siege style to control a stronghold or a camp. The zone normaly will be pve zone but when the time come (I think about 3 time zone with Jp prime time, US prime & Eu prime time) the zone will become pvp and the FC who register to attack a camp are allow to capture it, the other can register to defense, and those do not wish to register to attack or defense, are allow to mess thing up by join the pvp or wait until the siege time is over. The siege time can be 2 to 3h

3. On top of those 2 options, SE can add in duel system, allow player to duel and test themself every where but dungeon & raid. Of course SE will add in system in option allow player to auto deciline duel right ?