Is this definitely confirmed? How will a player be chosen to become Emperor, and what tasks and perks will being Emperor involve..

I haven't been keeping track as well as i should have been, plus, doesn't having a new emperor every now and then sort of lore breaking?

Yes a player will be crowned Emperor.

We have no details on how that will be done.

I will be emperor.
And you will be my slave

http://elderscrollsonline.com/en/game-guide/the-alliance-war

Ah, apparently the highest-ranking player of the Alliance that has taken the Imperial City will be crowned Emperor until another faction takes over (and possibly another player achieves a higher ranks) and the Emperor get's bonus' etc in battle.

I was also going to ask will there be an emperor per server shard, but i believe PVP brings everyone into the same shard..