I hereby suggest adding an "Enemy list" to the game:
- Basically works like the friend list. Both players have to agree.
- Players from then on inflict some (50%?) "friendly damage" on each others.
(Of course there's no reason why your "friends" can't be your "enemies" too...)

Possible Expansions:
- Let everyone choose how big a percentage of the damage they would like. Between each two "enemies", the lower one (or the average) counts.
- Let guild masters add an "enemy guild" (both guild leaders have to agree of course)
- "Let enemies join" / "everyone's enemies" team option for team leader (hehe, surprise :D)...
- An option to enable the "my enemy's enemies..." mode. In SK, your enemy's enemies *of course* aren't automatically your friends - we're ALL just enemies here ^^
- trinket (or simply hotkey ;)) to use battle equipment in haven (only works against enemies of course) for more funny surprises (yes, I know... lag... but you WANT to watch and you WANT to participate no matter how laggy it gets, you *know* it! :P)
- Also I think my "possible expansion" ideas should be ignored because reading them again I think I probably got carried away, that would be a mess xD! The basic idea stands though :P

Maybe some random Story Elements and a chance to add another 200cd=30days item or something permanently available for tokens...
Protective Field Modulator (Item description):
This device was created by gremlins as a top secret military project to disable the energy fields that keep the knight's weapons from inflicting damage on friendly targets. *Luckily* it has proven unsuitable for combat use, because it requires to be linked with the energy signatures of both knights. *Unfortunately* that gave the gremlins another excellent opportunity to further undermine the knights economy by selling the devices to the ones that are crazy enough to voluntarily fight each others.

Just to make it clear...
I repeat: My suggestion includes BOTH players having to agree and each one being able to cancel the agreement at any time. Also using this feature should NOT be mandatory and would NOT bring ANY advantages at all (except maybe if you count "fun" as an advantage :P). No "ladder", no scores, no disadvantages from dieing (except the usual ones), no gain from killing, no "real" change to the game.