The latest Diablo 4 cinematic trailer from Blizzard features Inarius facing down Lilith, armies at both sides. While this footage doesn't show Tyrael's involvement directly, his creation of the Horadrim and involvement with the various Paladins of Sanctuary means he is surely involved. Light and dark clash upon the battlefield and the now-mortal Tyrael is somewhere in between Diablo IV Gold.
His presence will be felt through these intermediaries until circumstances require his intervention. Tyrael is still feeling the effects of destroying his Worldstone at the end of Diablo 2. That mystical artifact protected Sanctuary from Heaven and Hell, and he now stands as protector over the land in its stead. Tyrael doesn't appear to be leading any further incursions into Hell or even go further in the Pandemonium Fortress, where he might offer advice similar to Deckard Cain to those who are willing to listen.
Five classes playable in Diablo have been released so far and all of them are takes on options from earlier games. With each of the games that has been released so far has provided something different maybe Tyrael might become a part of the battle and help balance the sides by offering players the opportunity to acquire angelic or demonic powers , in exchange for responsibilities to Sanctuary. This sort of mechanism could be a natural progression from the multi-tree development that was revealed for the series.
It is unlikely that Blizzard intends to turn Angels or Demons into classes, given that the series focuses on characters caught between their way. As the only mortal who is caught between Heaven and Hell Tyrael finds himself in an exclusive position in the entire Diablo history. He's likely to be an equalizer in the story, maybe even as a voice of reason instead of a partisan as the past buy Diablo 4 Gold. Even when forced to take the side of his opponent, Tyrael has come to understand the value of mortals and that's why he'll most likely play a role in the events that unfold in Diablo 4.