The API endpoints /v2/masteries and /v2/account/masteries are currently missing the Icebrood Saga masteries.
In addition I'd love to have endpoints for Strikes, similar to the endpoints for Raids.
You might consider posting in the API Development sub-forum.
I just came here to post requesting Strikes to be added to the API. Hard to keep track what I've done each day. Something simple like the worldbosses or mapchests endpoint that just returns the name of the strike mission would be enough for me.