Mixed Editions in a 3 Node SQL Server Always on Availability Group I could not find any solid documentation anywhere, checking any of you have seen/built an AG that looks like below. Appreciate your responses. 

SQL SERVER 2016  


Primary - Enterprise edition 
Secondary 1 - Enterprise edition - with Sync Replication
Secondary 2 - Standard Edition with Async Replication


Thank you
You might missed that the Availability Groups are only available in Enterprise Edition. 

In you scenario (with mixed edition), you would neither able to do following AG Configuration:

Availability Groups
Required all replicas running Enterprise Edition  

Basic Availability groups (limitations)
It limit to two replicas only  

Distributed Availability groups
Standard Edition only support Basic Availability Groups and Basic Availability Groups cannot be part of Distributed AGs