Here are my proposed changes for some of the rules:
1) Regarding Vanishing Dye, if both players agree, then it should be allowed (I don't want to have to redye my gear just for dueling and I'm sure most other players don't care).
2) DH vs WD: Currently, the DH will have no trouble utterly crushing any WD with these rules. I propose the WD can only choose two of the three: Zombie Dogs, Spirit Walk, Spirit Vessel.
3) DH vs Wiz: I recently played a good Wizard and he can kill me in 3 crit thunder bolts, and not to mention his other skills that hurt a lot. Also, his EHP was high enough that it took 3-4 hits total to kill him with Force Armor. I propose DH can only use either Battle Scars OR Companion, but not both.
4) DH vs Monk: I think the proposed change is ok but I fear for the 90% stacked dodge Monks. All other classes will have an attack which bypasses dodge (Rend, Haunt, Exploding Palm, Ray of Frost/Blizzard/...) so they won't have this problem. I think it will basically become a duel of RNG with the Monk to land your attack. Are there other solutions, such as banning Sharpshooter?