And Blizzard outright said the first two years, 4th (Initial test of achievements) and 5th (Kind of a milestone) were the only pets.
Blizzard outright said last year, the year before, and the year before that, that we won't see new special rewards til milestones. Milestones like 10 years. Which is coming in 1 year. And my money says they will have to say it again this year.