I just noticed a thread on the US forum that pointed to a Blizzard AMA on reddit (it’s the first post on the hearthstone reddit).
here’s the response from someone labelled as “senior game designer”:
We hear the request for auto-squelch, but still think it would be a net negative for the game. Emotes are implicitly good-natured, and we want to support them as such. Manually squelching can be used for the extremely rare outlier of toxicity.