Been running some sims just with the keystone casting, and it's not proc'ing Echo of Light like it does in game. It's so far down on my trinket list so I thought something was awry!
Here's a sim: https://www.askmrrobot.com/wow/simulator/report/99fd61994b8f4085b9acb39578ca7c60
I forgot to add the antorus trinkets to the list of spells that proc echo of light!
I will add those in our update today.