will there ever be an explanatiion on how David and Snow decided to name Emma...well Emma?

I believe that it means "universal".

I don't think that her name had any specific origin. She wasn't named after anyone. I think they just liked the name. In comparison, it's a bit weird how they wanted to name their son after someone, even before Neal's death.

If the time travel at the end of season 3 was always a part of the timeline, then maybe they'd have ended up naming her after herself, which is an idea I kind of like :) But I don't think that's the case.