We'll see in time, but I would really like that. One thing that minecraft needs is more paths to choose I mean once you finish the story (killing the ender dragon) it's over... With classes you'll have encourage to try rerun the game with another class, explore other weapons and upgrades made for that specific class
While we're at it, a set of skills like M&B Warband has would be a great alternative - not forcing players to stick with a class, instead being able to evolve their character the way the see fit.