I'm not worried at all aboud this.
In the real world there are alot of people that migrated around the world to.
So why should it not be possible in the elder scrolls online? You could RP an orc for example, lets say his grandparents migrated to morrowind, So his mother and he are actually born there. Then (around the time the game goes live) the allainces are forming (the allainces were not there in the past, neither will they be there in the future - something that other elder scrolls games prove). The allainces are only there in this particular timeline were TESO is situated.
The orc feels home in Morrowind, all his friends and close familie are there, so its only normal that he will fight for the Ebonheart Pact.
Thats how I see it.