PvP is an interesting mechanic for roleplay because it puts restraints on how your character acts and what he can do - restraints help to shape and define the character. In pure consensual text-based RP, involved players might interpret the outcome of an action differently on both sides, or they might go for an outcome that is not fitting optimally from their point of view to avoid frustrating the other player, or they might just disengage from the RP altogether if it doesn't come to a conclusion they will accept. PvP is a neutral arbiter that cannot really be misinterpreted, and helps to shape a common "reality" for all involved parties.
As a relatively new player, I find the etiquette around PvP a bit confusing or intimidating. I've been asked before to a battle, and declined because that's what my character would have done in that situation, but it felt less than satisfying than just being forced to fight in that instant (and there was still the nagging thought that not dying was more convenient for me as a player in that situation).
I would like to see more PvP possibilities (and less possibilities to avoid it), with perhaps different ways to "back out" of PvP in certain areas - such as surrendering to being looted of one non-quest item instead of dying (and gaining immunity from such PvP challenge for some time in turn), or perhaps the attacker himself being unable to avoid confrontations even in non-PvP areas for some time if initiating PvP.
It's also easy to imagine how unhindered PvP can motivate some players to play for PvP-centric dominance in some areas at great cost to new players. Perhaps new characters could group together and get an NPC guard escort to help them move along in the early stages to combat this (two travellers per guard minimum, the total level average may not exceed a certain amount).
It is clear that one's PvP behaviour (if not based on consent/challenge) must have consequences after the event. For instance, walking along your victims on market day in Hydlaa in plain sight is suspending belief and should be seen as bad RP (unless the killer was cloaked etc). It should be possible to track killings that weren't challenged (and for the victim to choose to forget them if he thinks the killer was cloaked), and if a certain number of recent victims are present, remove the PvP challenge protecting from the killer (and let the guards have some aggro, in extreme cases). After all, a single accusation might not count for much, but a number of victims with matching accusations will be very different.