In this post, Kainenchen talks about what she would want out of her ideal psionics system. I started thinking about how I would make that happen, wrote my initial thoughts in comments to that post, and let my brain percolate on it for awhile. I think there's a chance, by the by, that a system very like what I'm about to explain exists, but if so I haven't played it. This would be easiest to apply as a modification to the new World of Darkness or as an addition to Over the Edge. I would potentially remove Willpower from nWoD if I were going to use this system.
This system of Convictions is necessary for the psionics system in question because of the way K wants telepathy and empathy to work. Once such a system exists, there are neat ways to plug other areas of the system into it, such as making strong Convictions juice up pyrokinesis.
Convictions (not the legal kind)
Characters are motivated by Convictions. Normal convictions are rated on a scale of 1-5 (this is convenient in both nWoD and OtE). 1 represents a short-term or back-burner desire, while a 5 represents an all-consuming drive (perhaps related to killing a six-fingered man). Players receive a budget of Convictions at character creation - let's say 20 points, with cumulative costs (level 1 is 1pt, 2 is 3pts, 3 is 6 pts, 4 is 10 pts, 5 is 15 pts).
Conviction represents a pool of bonus dice that players can spend to improve rolls. Each point of Conviction might be two bonus dice to a single roll in nWoD, or one bonus die to a roll in OtE; these pools refresh at the beginning of a new adventure (since the pools are bigger than I would want players to run through in a single session). Spending Conviction to improve a die roll does not change the permanent Conviction score for purposes of mental defense or other applications.
More importantly (for my original purposes, anyway), Convictions also improve your defenses against psychic tampering. From K's description, one of the main ways a telepath or empath influences a fight is by understanding the opponent's thoughts or emotions, and then rewriting or redirecting those thoughts or emotions. It's harder to influence the thoughts of someone who is deeply invested in what he's doing. For nWoD, this can be applied as a penalty to the telepath's roll. If Resolve or Composure also apply, as they usually will, you'll want to factor in about a 1-die constant bonus to the telepath's roll, just because a Conviction of at least 1 pt will apply as a defense so much of the time.
For OtE, it'd be a little more complicated, but that system isn't exactly driven by fiddly rules. Influencing a character away from a Conviction has an increasing target number. Influencing someone with no applicable Convictions might be around a TN of 3 (66% success for a character with 1 die in that fringe power). This scales up at (3 + the point cost of the Conviction) therefore 4, 6, 9, 13, 18.
Convictions can change over time, of course. I'd suggest allowing a character to purchase new Convictions with XP, and re-spend old Convictions at a rate of 5-10 points per adventure. Fulfilling a Conviction (killing the six-fingered man) might do all kinds of good things for you, starting with letting you convert those Conviction points directly into bonus experience points earned from the story goal. (Incidentally, this models people not knowing what to do with themselves once they've completed their major life goal. They could spend all of those experience points on some new Conviction.)
Morale and Rage: Temporary Conviction
You could also have some Convictions outside of the character's purchased list. Newly implanted desires, inspiring speeches, or getting screwed over in a way that demands reprisal might all be awarded with a new 1-2 pt Conviction.
When your side is flagging, a charismatic leader might be able to rally his troops, granting them new temporary Conviction (nWoD might handle this with a Presence + Persuasion roll, as per Oratory; I'll have to think a little more on how this should work in OtE).
FATE and Mutants and Masterminds are the first two systems that come to mind for me that give players a minor bennie when the GM does something at least partially by fiat that really screws them over. This system could handle a similar payoff in the form of a point or two of temporary Conviction. If the player doesn't get a chance to use these points by the end of the adventure, it can become a longer-term goal, and I'd let the player cement it into a normal Conviction at a reduced price in experience points.
You could even use this as a rage mechanic, granting the temporary Conviction "I want to hurt him back!" every time a character takes damage. In nWoD and OtE, characters don't have large health pools compared to the amount of damage attacks can generally kick out, so I'm not _that_ concerned about characters wanting to get hit just for the extra attack dice they'd get the next round. Therefore I'd be more-or-less okay with this Conviction getting used more times in a fight than its value would seem to indicate. It stays a low-value Conviction, though, because the character doesn't become vastly harder to influence.
Pyrokinetic Passions (which is not a new Eclipse romance novel, but it should be!)
I also think it's pretty cool if telekinetics, pyrokinetics, and electrokinetics get their relevant Conviction as a bonus to their die pool whenever they can apply it. This would certainly fit theme well. In nWoD, this would generally have the effect of putting this kind of attack effect more on par with mundane weapon attacks (ahem, setting aside how much you can juice up a rote in Mage). In OtE, this would put your attack from a fringe power equal to or better than an attack from a normal weapon, and I might go with (level 1-2: +1 die, level 3-4: +2 dice, level 5: +3 dice).
Psychometric Sentiments (a new line of psi-print greeting cards produced following the Blue Sun's buyout of Hallmark)
The whole theme of postcognition is that objects carry psychic resonance from prior owners. That's exactly what we're talking about with Conviction. Whenever an object is used for a task relating to a character's Conviction, especially if that character spends Conviction for bonus dice, the object is imprinted with a strength equal to the character's Conviction. Obviously, a GM wouldn't actually track this most of the time; this is a guideline for use after the fact, not a rule to be tracked during play. The difficulty of postcognition on the object is based on (6 - Conviction level). In nWoD, that number indicates successes necessary on a postcognition roll. In OtE, the value of (6 - Conviction level) gives you your difficulty: 4, 6, 9, 13, 18.
I'm aware that this post is a bit jumbled and jargon-y, but if it makes sense to you, let me know what you think.