Does anybody know about how your choice of race and alliance affects the main questline?

Like will the main quest for members of the Aldameri Dominion be different from that of the Daggerfall covenant and Ebenhart Pact? And if your race affects your role in the main story, like if you choose a dark elf and you start in morrowind, will your questline be the same as a redguard in Hammerfell?

alliance choice will. not sure about race.

I think race only affects dialogue and NPC attitudes towards you. Alliances all have their own questline separate from the Molag Bal quest, I'm pretty sure.

This is actually all unsourced, vague recollections of months of information so don't take anything I just said at face value.

Will the faction PVE areas each have their own quests? Or will they be mirrors of each other? – By El Hefe

Each Alliance (and area) has its own completely unique quests and storylines, layered on top of their individual internal struggles and history. When we design content in The Elder Scrolls Online, we aspire to create storylines, experiences, and characters that are befitting of the Alliance they are a part of. Each Alliance’s content in ESO is as varied and dynamic as the Alliances themselves are—your adventures an Argonian in the Ebonheart Pact, for example, will be quite different than those of a Bosmer in the Aldmeri Dominion.

Should you choose to play characters in each of the three Alliances (and we hope you do!), you will experience completely different content that is representative of each Alliance’s story, history, and politics.

http://elderscrollsonline.com/en/news/post/2012/11/13/ask-us-anything-ebonheart-pact-part-1