PvE Campaigns
The Mega server technology wouldn't change, this just places people into more speicalized groups.
Regulation Campaign - This is the standard ruleset of ESO. It is in this space you play the game how they intended.
Private Campaigns - This would be like you playing ESO unpopulated by players. Your Private Campaign is linked directly to the Regulation Campaign. New perks would be added over time such as housing, titles, or marriage. You can move between Private and Regulation Camps by shrine points and even invite guests to join you.
Exploration PvE Campaign - This would be an open world, no restrictions. There is limited NPC interaction, freedom in other faction's territory, and a few NPC wandering mobs. It would be a non-combat campaign and you could travel through Cyrodiil unharmed.
wPvP Campaigns
Everyone who wants to play in world pvp can join in three ways;
Home Campaign - This would be like regulation campaign but you are flagged for wPvP. You can still quest and level like you normally do except there would be enemy players around.
Invasion Campaign - This would allow you to play in another region against players your level. You would have to be careful of cities but you can sneak around and try to ambush willing players.
Exploration wPvP Campaign - This would be limited to all areas outside Cyrodiil. You can explore around but will be attacked by opposing faction guards and players.
Modify Campaigns
You may play on Specialized Campaigns that have different modifiers. A few examples would be;
Open Race Modifier - Allows you to change the appearance of your character. You would still be the original character in all PvE context, you'll just look different. Players who do not have this modifier on will just see you as your original appearance.
First Person View Modifier - This Modifier places players together who wish to only use First person view.
Player made Modifiers - After some time developers could allow players to make Modifiers and 'host' games for people to join. There would be rules and guild lines such as no modifying attributes, xp or coin adjustments. Players could tweak dungeons and make them harder, add the need for food and water, add weapons and armor, and many other nifty things you're allowed to do with TES mods.