Check out our blog post we just posted going over this 10.3 release here:
*Currently Android is out in the Google Play Store now. iOS is making its way through the App Store and will be out soon.
I would be keen to see documentation, too. I am planning to use this feature and am ready to start preparing my dataset. I could start this immediately, while I wait for the iOS version to update.
We are working on a blog post series going over the features just added to this release. Some tips for the related record support
ESRI states that it will be released after it finishes the Apple App store review. Rumor of this week into next week.
I have to say that I am extremely pleased with the recent update that supports related tables on android, but I'm patiently awaiting the iOS version also.