Azure AD Pass through authentication roadmap/GA?

There is no official roadmap that provides specific dates for the availability of features for Azure Active Directory and Enterprise Mobility + Security. You might hear estimations during events or in 1-1 discussions but as i said there is no web site that you can see dates for GA of features.

The Public roadmap site only lists features (no dates or estimations) that are currently in public preview or recently avaiable in GA https://www.microsoft.com/en-us/cloud-platform/roadmap-public-preview

As others mentioned in this thread, Azure AD Pass-through authentication is currently in public preview since last December. The team is working hard to incorporate the feedback and be able to GA in the next few months.