If Cyrodill has say 10 different 200 player areas instanced does that mean more then one Emperor can be crowned at the same time? If this can be done it kind of defeats all the good aspects of the mega server right there because it makes PvP or RvR cheap and meaningless.

I am pretty sure the whole thing with Cryodill is being handled slightly differently than the genral auto-sharding of the "realms" or pact lands.

There was a news release about pvp being done in Campains like how wars are fought with multiple fronts or something. It may address these type of issues. But yea it is still a good question with respect to how long someone stays emperor and how often on of these pvp campains completes to crown one.

There will ultimately be no "emperor" crowned (at least any that will last for long), for canon already dictates that Tiber Septim (or Cuhlecain, "Emperor Zero" if ya wanna get technical) will be the next emperor of any note after the end of the Akaviri Potentacy. It's called an "interregnum" for a reason.