Is finding out what the deal was with Mare, is that an Era 2 thing we're going find out or is that...
No, unfortunately it is to be left, probably, as a mystery. It is a minor secret that I do not consider a major Cosmere thing, more of a backstory thing. I might eventually get around to it. The chances of it factoring in are very, very slim. I stay closed lipped about it because there is a part of me that thinks I will work it into Secret History 2, sort of like flash-backing material, but I'm not 100% sure I will.