Too easy to exploit.
Duel only friends that comes to let themselves die at your hands and you have un unstoppable grind machine (easily spottable in the long run ofc but even then..).
lol?
If it was anything like it was before it would take you way longer to make XP dueling than just going to battle or siege. xD
but okay then , I'd enjoy watching 2 people waste their time so that one person can level though I doubt anyone would do this because.. well for the reason I already stated, not enough xp to be made this way, it'd be faster to go to Battles or Siege.
all in all, I say YES to some xp on duel servers, I don't see a problem with getting a small reward each time you win, I HIGHLY doubt that this could be abooooooooooooooozed simply because you wouldn't make enough xp for it to be worth the time to abuse.