I was thinking of a way there could be a self policing DA, but I just couldnt see it without some new coad. So here goes.
Arena setup
KillShooter ON
Duelmode ON (new parameter)
All airfields are country 1 (doesnt include V bases)
How it would work
To disable killshooter with another player, just tune to the same number vox channel. There is already a game function in place to change the icon color of the person you are tuned with giving you a visual confirmation of who is able to engage you. For more flexible functionality, a 'duel' icon type would be a nice touch. To close an obvious loop hole, there would be a delay between the time a player de-tuned, and when they are disengaged from 'duel mode' (ie. you cant just retune in the middle of a fight to keep from being shot). Another nice touch would be a request/accept command to automatically tune you both to a random channel.
Pros
Materially uninterupted:
1v1's
KoTH's
2v2's (with the use of .wingman to hilight 'friendly' icon)(another nice touch would be multiple wingmen for larger duels)
Round robin dueling
Private lessons
Private squad functions (especially if squad channel counts as duel mode)
No vulching (if you take off in duel mode in front of someone that will vulch its your bad)
All loopholes left by using 2 or more countries are closed.
If someone is bothering you or your party, retune, there are many channels.
You always know who is able to engage you.
Cons
Other than valued coad time, I cant think of any.
Feel free to make a cons list.