If there is a fallen guardian in the lore where and what is going on with them
Edit:if there is no fallen guardians then who do you think it will be my theory is chelchis kell of the house of stone if he wasn’t taken
Most likely either post light fall or final shape.
Same for cabal.
If I had to guess, post final shap we will see a relaunch of D2 (instead of d3) which will update the engine and make the game purely next gen only. During then we will see the 2 new classes added.