I thought RvR was more of a gameplay type similar to something like planetside or PotBS where you choose a side and that plays a leading role for gameplay because the point of the game (or atleast end game) is fighting an enemy team. gameplay revolves more around fighting other factions instead of just having clan wars (like micro factions where there is flexability and optional play) and further differentiated from games that use supposedly warring/opposite races that never comes into gameplay (like rappelz).

one server fighting another I don't think really exists because that would cause latency and connection problems usually you all connect into one place. I don't thing one server being connected to a particular team in connection to another server denoted by another team ever actually exists. - I see major limitations of this working on a technical level and not actually being attempted before.

imo my favorite RvRs haven't been mmorpgs because reaching end game strength to be effective in battle seems to limit the overall scale of the battle. No fun in a battle where no one shows up because it's just gonna be a few high levels - battlefields swarming with chaos with multitudes of strength (related to skill rather than how much you grind) is more my style