Vulpera are surely coming. Only reason that they did not come yet is cus blizzard wants to use them to sell the next expansion. No other allied race has gathered so much traction since bfa beta days. It was a strategic decision to hold them back to sell more exp packs.
They are controversial (which blizzard loves) and they were single handedly the most talked about thing the entire expansion. cant think of anything that generated more buzz in the official forums, like, ever. They also made sure to never answer a single vulpera question in any of the Q&As on purpose...dont wanna ruin the surprise.