One idea that comes to mind for me is an option for a person to 'watch' other people battle and then get some secondhand experience from that. Essentially learning by examining how other people engage in combat without having to do battle yourself. The player actually doing battle would not lose anything at all, they would get the exact same amount of XP as if they had fought alone. But the person watching would get a little XP by watching the battle (maybe like 1/10th of the normal XP value).
It would basically be like a person watching life-action footage of combat or spellcasting or whatever. You can learn from that to provide the experience to train your own skills later.
Some people may say that this would encourage powerleveling... or at the very least a bunch of people parking next to a high-level monsters spawn point and then watching other people fight it. Which actually could provide a little bit of atmosphere... all those seats (or stairs or whatever) in the Arena might actually have people in them if there was a reason for people to sit there. Let people sit back, watch the combat, and get a little experience for free. People could chat and roleplay while watching the fights if those fights could actually be exciting.
Plus, letting people get experience through watching could help make healers a bit more practical in the game. Right now, I don't think a dedicated healer can get any experience unless they actually help kill a monster or mine ore or whatever. If a healer assists a fighter by healing them. They could watch the combat and get experiece from that. It shouldn't hurt the fighter in any way.
Another problem is, that the whole concept of actual experience is really getting weird in games like this. Its almost treating experience like a resource that you can only get by killing animals. If instead experience was rewarded for each action in battle (such as each strike of the sword) then kill stealing would not really effect people as much. If you bring a monster down to 3% and somebody swoops in and kills it, you should have already gotten all the experience from that previous 97%. He might get the XP from that 3%... but who cares? You already got your XP and they can't steal that from you.
There is already the code that lets people gain practice points for each combat action (like attacking with swords or axes or melee combat) a little change in the code should be able to let people get their experience points from actions instead of just from killing monsters.
So, make it practically impossible for a person to steal experience from a person who worked hard to get it... then create a way for people to gain experience by just watching the combat. Killstealing would not only be difficult to pull off, but it would be pretty unecessary.
As for the loot... eh not sure how to deal with that.
