A Quakecon panel showed off video of new zones coming to The Elder Scrolls Online, and discussed what players may do in them (and to one another), particularly with regard to a "justice system" coming to the game.
When that arrives, players will be able to commit crimes — and suffer the consequences for them, of course. This introduces things like stealing and bounties, which have been features of the standard Elder Scrolls RPGs for some time. Additionally, players may now murder NPCs, and when guards arrive to collect the bounty or haul you in, you may find that human players are leading them, adding active world PvP to the mix.
This is the video explaining justice to panel-goers at Quakecon 2014:
As for new areas, a new Imperial City will be added to the game, unlocked once the player acquires the Cyrodiil Keep. Imperial City is an area ruined by the planemeld of Daedric lord Molag Bal. Players will be on a mission to capture and hold different districts of the city (enabling respawn in them) as they clear out the enemy alliances and Daedra, who have thrown Imperials into the arenas for gladiatorial combat. For more, see this video:
Players of The Elder Scrolls Online will find much more information about the panel at the link, including notes about improvements to the game's grouping system, dungeon scaling and repeatability, and a new veteran dungeon, City of Ash, coming in the fifth update: