I don't think they need to add new vocations or abilities, though. There's a good selection already.
Disagree
There should be at least the remaining advanced vocations for Thief and Archer
Mystic Spearhand has more in common in playstyle with Thief than it does with Fighter or Warrior. Thief has unbeatable personal defence (while it has stamina) with obscene DPS. Spearhand had obscene team defence + extremely high damage output with its basic attacks.
Magic Archer is the magic + archery advanced vocation.
What would an advanced version of the Thief vocation look like? An even more broken version of Thief which is already one of the strongest in the game?
In DDDA Ranger and Strider had pretty similar skills with Strider having a melee emphasis and Ranger focusing on bows. There are no such overlaps in the skill sets of vocations this time around, they all have distinct playstyles.
Warfarer allows you to build pretty much any hybrid class you want to play as already, I don't see that you'd need another way to play Thief + Archer advanced vocation when you can set it up to play that way if you want to. It's basically a much more versatile version of Assassin.