Sourabh Agarwal points out some new reports in Management Studio 17.4:
The Latency data collection functionality and the associated reports allows a database administrator to quickly discern the bottleneck in the log transport flow between the Primary and the Secondary replicas of an Availability Group. This feature does NOT answer the question “Is there latency in the Availability Group deployment?” but rather provides a way to understand why there is latency in the Availability Group Deployment. This functionality provides a way to narrow down the potential cause of latency in an Availability Group deployment.
There are some things that this report doesn’t capture, but it does give us a bit more insight.