The mainline Diablo series hasn't seen a new class for 10 years. The spiritborn, coming in Diablo 4's Vessel of Hatred expansion on October 8, are an entirely new class for the series who fight with the power of animal spirits and only slightly resemble classes from prior games, like Diablo 3's monks.
Blizzard deliberately created something new to keep Diablo from getting stale, associate game director Brent Gibson told PC Gamer in a recent interview. Even if that means fans will continue to beg Blizzard to add paladins one day.