At server release, 100 alliance and horde lvl 1s would meet each other as they were heading to each others zone in stv waters between booty bay and westfall. Actually more like 1000

. Later on you would see world PvP campaigns all over azeroth, various defense and offense wpvp guilds being created, for 2 months there wouldn't be a guy to reach lvl 30. Events with 200v200 happening in durotar and elwynn etc, later on everyone would raid cities and fail to do so cause of dedicated defense.
Humans and orcs would be most common.
Most played classes would be - Warrior, Paladin, Shaman
Average - Rogue, Hunter, Priest
Less played - Mage, Warlock, Druid
Everyone would run around in greens or PvP gear. Battlegrounds would be a little more active than they are now, half of them being guild vs guild premades to show superiority. Guild leaders of popular guilds would be carried to r14 by solotagging faction bosses. (If they ever managed to get there without getting 80 defenders up their ass) (and BTW faction leader gives 15k honor) basically an RPPVP server with world PvP raids and events happening constantly. Also most people would flag themselves just for the faction insignia on their portrait.
Imagine kul tiras base in durotar being filled by humans, constant war would happen between tiragarde keep and razor hill and similar scenarios would occur in every zones.