I have some ideas to make rogues more useful in PvE and PvP that I didn't see in the list. Sorry, I'm a bit late to the party.
My lines of thinking are more directed around the idea that a rogue's fighting style and tactics interfere with his opponent, and as such aren't targeted around formation as much, but instead are directed towards the idea that a rogue is skilled at fighting in unexpected ways that his target doesn't expect, and by striking vital points can weaken the offensive and/or defensive capabilities of both A) his melee targets while wielding a finesse weapon, and B) his circle stab/hamstring targets.
Why are rogues currently weak in PvE? Because they don't do more damage than a warrior class, they cannot ride front rank, and they're vulnerable in the second row to reaching PvE NPCs.
Which of these can/should be changed? For one, I don't think rogues should be able to deal more damage than a warrior class in a full on brawl, so the raw damage output of a rogue shouldn't exceed that of a decked out warrior/barbarian/swashbuckler. For not being able to ride front or second rank, there have been good skills already suggested like divert that would do a good job there. I personally love the idea of divert: The same as tumble but that doesn't change your formation, but that unlike tumble is only able to divert one target at a time. However, I would suggest some sort of limitation on divert in the form of a cooldown on the rogue or on the target to prevent it from being able to be spammed. I'm partial to the idea that if a rogue diverts the attention of an enemy, that same rogue should not be able to divert that enemy again for 10 combat rounds. This would make it useful but not godlike in PvP while avoiding silliness in PvE.
Now, as to the damage side: What about some options that could allow a rogue to add damage or limit the enemy meaningfully without just adding raw damage? I think there's an entire world of potential status affects that a rogue should be able to reasonably apply to an enemy that, while not increasing his own raw damage output, could not only make a rogue useful but potentially even desirable in PvE.
Here's two thoughts.
Quote:
A) Wounding Blows.(1-2% PE cost at GM)
A rogue excels in using underhanded and unexpected tactics during a battle to make up for his lack of raw strength and battle tactics. Usage: While in melee combat with a finesse weapon, a 1-round lag which targets the rogue's melee target will deal minor damage to a targeted portion on the enemy (head/chest/right arm/left arm/etc) and cause all further physical strikes from -anyone- to the affected area to deal 20% extra damage for the next 3 combat rounds. This skill is also automatically applied to targets of the rogue's backstabs, circle stabs and hamstrings, causing chest or targeted leg damage to be increased on a successful hit. This bonus does not stack, but repeated applications of expose weakness will refresh the duration of vulnerability on the targeted body part.
Ex: Wound (right arm).
This skill is automatically checked for victims of circle stabs, backstabs and hamstrings.
Quote:
B) Interrupt/Harass.
By devoting his attention entirely to a single target during combat, a rogue can interject himself into the movements of the enemy precisely when it is most devastating. Targeting a victim (PC or NPC) for harassment takes 2 rounds of focus on the rogue's part, after which point any combat skill used by the victim, magical device activated, spell cast, or potion quaffed has a small amount of delay inflicted by the rogue along with some minor damage (Every combat or defensive action takes an extra combat round to perform). A rogue can focus on anyone as the target of his harassment, but he will only be able to hamper the actions of his target if he is either A) in melee combat with the victim or B) able to circle stab the victim.
Harassing a target prevents the rogue from targeting any other enemy with combat skills like trip, circle stab, hamstring and dirt kick, but the rogue can choose to stop harassing a victim (no lag) or otherwise start to focus on harassing a different victim (2 round lag again) at any time.
Those are my two initial thoughts: Giving them a unique damage amplifier that applies both to themselves and their party would greatly help their usage in both PvE and PvP while fitting with their theme, plus it would look kinda cool to see "Valtari strikes Slayne, leaving an exposed wound on his right arm!" during combat. In addition, giving rogues an extra mechanic for slowing down combat skills of a dedicated single target in both PvE and PvP would also add to their attractiveness in both endeavours. By having harassment require more upfront lag than circle, it gives the rogue a choice to make as to whether it's worth the dedicated attention for any given fight also. I think it would also make a rogue more rewarding and engaging to play.
I think those two skills plus divert would probably make rogues perfectly competitive, if not perhaps too powerful for the health of the game.
Maybe some more thoughts later.