Having the ability to create triggers on ChangeEvent is awesome. But I found this small limitation while I was playing with the ChangeEvent of OpportunityContactRole. It seems like the IsPrimary field of the OCR object is not a part of the Message Structure. I updated a contact to Primary, and this is what I got as a response.
client=SfdcInternalAPI/; getCommitNumber=10700208387922; getCommitTimestamp=1562529561000; getCommitUser=0056F00000AbEzTQAV;
getDiffFields=(); getNulledFields=(); getSequenceNumber=2; getTransactionKey=000146f2-73ad-fd0d-347b-0c2ff93e950f;
LastModifiedDate=2019-07-0719: 59: 21, LastModifiedById=null
As you can see, IsPrimary field is not available which seems to be odd. Having this would really simplify a lot of things.