Given the latest patch, the biggest issue players have is that Taunt is basically acting like Charm.
If you or one of your companions is taunted, then the player should still have full control over the character. AI should not take over. If you're taunted, you should still have full control of the character, and be able to cast buffs/heals upon your companions. However negative effects/damage dealing skills should only be targetable upon the enemy toon that landed the taunt. Heck, even make sure the character can't move away from the taunter, but only toward (if they so choose to move). But no, Taunt shouldn't be a Charm mechanic.
Granted, it's a "limited" charm in that it will still attack an enemy, it's likely to burn skills you don't want set into multi-turn cooldowns.
Case in point, enemy casts shackles on a toon, then gets a guaranteed taunt on that same toon. You lose every option to NOT attack that toon if the AI takes over. And you watch as your toon kills itself.
I just posted about this on the Steam Forums not yesterday.
My solution is very similar to yours in that a Taunted Playercharacter should ONLY be limited and allowed to attack the Taunter and all other targets are invalid.
I would even go as far as to say other party members are also invalid as to force the player into attacking the Taunter or doing nothing (effectively loosing a turn which also has tactical value to the battle).
I would be okay with not being able to cast buffs or friendly spells on your party during the taunt duration as the character is supposed to be enraged or focused on the Taunter specifically.
I 100% agree that under no circumstances should Taunt release control from the player.
Even more so with the new update to taunt costing 2 action points but circumventing ALL armors.