Currently, there are very specific ways to hold threat: Run with a frost staff and heavy attack, run with sword&board and use Pierce Armor, etc.
Instead of forcing very specific builds in order to properly tank, we should simply have a Taunt ability. Perhaps under the Fighter's Guild.
TAUNT: While activated, any damage you cause to X enemy(s) forces them to focus on you for 5 seconds.
The "X Enemy(s)" portion could begin with just one enemy, and up to 10 enemies at level 4. (As each skill has 4 levels of training.) Worded this way, we can see that a Tank could loadout any way he saw fit, and it would give him the ability to go back and forth between single-target attacks to hold aggro on just a Boss, or use AOE abilities to hold aggro on multiple mobs. The Taunt ability could Morph to give the Tank more options such as:
Hold the Line: Your Taunt now holds an enemy's focus for 15 seconds.
Defenses Up: Enemies you have focused on you deal 5% less damage.
The first morph would help DPS tanks, while the second would be more beneficial to shield tanks. Anyhow, just an idea.