A student mentioned an experiment by Linda Acredolo and Susan Goodwyn in which young children were taught Baby Sign, a simplified version of sign language for children who have not learned to speak yet. The children learned to speak much faster than the control group. In passing, the student mentioned that the Baby Sign kids did not have "terrible twos" because they did not have the same frustration in communicating that other toddlers did.
Which gave me an insight about why the Gruntled kids did not go through terrible twos. The Gruntleds, you may not be surprised to learn, are a very talkative family. "Hypervocative" is the term we use at home. The children were talked to constantly and with a fairly grownup vocabulary from birth. The kids, given their mixture of nature and nurture, were perhaps over-determined to be big talkers and amusing conversationalists while still in diapers. Thus, if terrible twos are caused by an inability to communicate, talkative toddlers should skip it.
It is certainly worth a try.