Board Thread:Naruto News/@comment-945885-20150423073012/@comment-5832352-20150505163959

Another possibility for Sarada: Karin acted as a surrogate or donor mother.

Sasuke settled with Sakura. Karin couldn't have Sasuke. Maybe something happened to Sakura to where she couldn't have children. Something was happening to Karin where she wouldn't be competition for Sakura (dying, prison, new job). Both girls were quite intent on continuing the Uchiha clan.

So ... Sakura and Sauske get married. Karin agrees to get knocked up so Sakura can play mommy.

Maybe the reason why Sasuke has been gone so long is that he's still squicked out by the whole thing.