I think there are 4 ways they go. Before I list my thoughts, I think alot of people thought or still think Amazon, I’m going to say I don’t think so. One of the main reason I think is that with no gender locks in D4- there isn’t such thing as a “male Amazon” version. They could maybe create a male type but I feel its highly unlikely they do.
Necromancer: Probably (arguably) the most popular class in both D2 and D3 that it would be a disservice to leave it out again like they did at D3 launch. There is no current Summoner class which makes Necro a viable option.
Paladin/Crusader: While the Barbarian can wield a shield, one of the things that make this class unique is the shield as not only a staple but its identity and ability to use it also as a weapon. The other thing that makes this class a viable option is there is currently no holy class.
Creating an entirely new character: One of the ideas ive heard by some streamers on YT was a priest summoner. In a way it’s almost like merging a Crusader and Necromancer as a new character. Another idea ive heard was a “Death knight.” I think this is a viable option because it stretches creativity for the Diablo franchise-a class never seen before really keeps things fresh for fans and the game.
The Warrior- a remaster (or remake) of the original class from D1. I see them taking this route with the introduction of the other two D1 classes- Rogue/Sorcerer(es). In a way it makes sense that they go back to the games roots and reintroduce the original 3 classes in a new era and generation that never had the pleasure of playing D1. This also gives the Devs a chance to be creative and modernize the 3 original classes into something unique.
The Warrior is my prediction.