I don't really think we'll see a Worgen allied race. I don't think Blizz has specifically set out to make one for each. I mean, if they are, then it would probably be Drakonid for the Horde and a bear race for the Alliance. Probably that Furbolg progenitor race.
Like I said though, I doubt they'll do a Worgen Allied Race. My guess for the next part are Mogu to join their fellow Titanforged races on the Alliance, and Ogres for Horde. As Ogres are a stonebound race too, and would be a nice Horde equivalent of the Bulky Kul Tirans, who were originally planned for much later. Would also explain Rexxar's place in BfA.