Five Diablo 4 Gold playable classes have been announced so far each of which different versions of the previous games. With each of the games that has been released so far has brought something new to the table and exciting, maybe Tyrael could become a hand in the battle and help balance the sides by offering players the ability to gain angelic or demon-like abilities in exchange for duty to Sanctuary. This sort of mechanism could easily follow on the multi-tree progression that was already confirmed for the series.
It's unlikely that Blizzard will make Angels or Demons into classes as the franchise focuses on the people trapped between their ways. In reality, though, as the only mortal in the middle of Heaven and Hell Tyrael has the most unique position in the entire Diablo the lore. He'll likely to be a balancing act throughout the story, and maybe even an impartial voice, instead of taking sides like previously. When he's not forced to pick sides, Tyrael is now aware of what is important to mortals, which is how he will most likely participate in the events of Diablo 4.
Blizzard's method of speccing your character in Diablo 4 is a blend of the style of the studio's Diablo 2 and Diablo 3. As executive producer and director of the Diablo franchise Rod Fergusson put it, "Diablo 2 felt like you were locking into the game; you could respec once per difficulty. But with D3 you kind of changed your look like you changed your clothes. Everything was gear-based as opposed to skill-based."Fergusson added, "I think the fact that we have skills on the equipment in buy Diablo IV Gold is really nice for experimentation -- as a sorceress I [might] get Blizzard [on a pair of boots] three levels before I should and I can try Blizzard to see if I actually want it."