I agree failing the perils of the warp test should cancel the power. Makes things a bit riskier. I really don't like the loss of 3D10 willpower though especially as you're planning to use the same difficulty modifiers as for the psychic test. That puts us back to the situation where one failed test means no more psychic powers for that game, thus discouraging purely psychic characters.
The thing to consider about this is that this is the only way in IRE that characters are commonly likely to lose Willpower, characters can recover Willpower, and generally Perils are massively less likely than in the LRB.
A character has to be doing things like throwing around Psy Rating 5 powers at around a ~30% chance before they're in the same ballpark for a chance to trigger Perils of the Warp as fail a risky action.
And this is still assuming that the Psyker doesn't have the new "Favoured by the Warp" trait, which is intended to help protect characters that really have very little in their arsenal but Psychic powers (such as my own Maya Avens, who other than having about thirty psychic powers to choose from has a compact laspistol and BS 47).
In this case (assuming no Favoured trait), the expected Willpower loss for attempting a Psy Rating 5 power at 30% chance is 5.8 Wp. (Averaging all possible outcomes, both successful and failed).
Trying it under the LRB, (for which we have to assume a Speed 4 character, because Risky chances vary with speed) and that expected loss is 11.4 More or less double, which comes from possibilities like a ~7% chance of passing the risky action, but then failing the test by 60 points or more and thus losing 6D10 Willpower.
As Perils is now the only one common source of Wp loss, I thought I had to turn it up a bit, because to be honest, even rolling badly on 2D10 Wp loss isn't
that disastrous to many psykers.
Not a fan of persistent powers being hazardous. It might only be a low chance but it will penalise any pure psychers who are heavily reliant on psychic defences to stay alive (such as the old Isabella, before she was warped in the recent campaign).
I'm not absolutely certain about it myself (so perhaps it should be in orange text), but IRE is still an work-in-progress project being written primarily by a single person - the only large playtesting team I have is the community. Otherwise it's just me with spreadsheets, and occasionally playing against myself.
While the theory and spreadsheets are often effective, they don't give an exhaustive sense of how something feels on the table - never more so than with IRE's close combat rules, where somehow I ended up being surprised when the rules did exactly what I'd designed them to.
This means that some of the rules that make it into the release versions are experimental - things that
might work. If they don't, then the hope/expectation is that players will give feedback and then house rule them until the next version.
The thing is, it does feel "realistic" that maintaining a power while under the stress of a combat situation has some risk (beyond simply failing to maintain said power), and now that borrowing the Psychic Phenomena system from Dark Heresy offers a mid ground between "Nothing" and "Your brain explodes"
If it proves too problematic, it might be tweaked - possibly into a "Mini-hazard", possibly by making it so that it's automatically Phenomena rather than Perils, or whatever - or removed, but one of the problems with IRE so far has been that psychic powers can become quite dominant.
Nullifying a persistant power is a good idea, although I think it should need line of sight.
Nullification has a 5 yard range and characters will still need to be aware of their target, so I don't imagine that's a major issue.
Not sure about resist for non psychers. Most of the powers that target people have some sort of resist built into the power. Will this be as well as that or a universal rule instead of power specific ones?
This is a universal rule (and actually existed in the last version of IRE). The issue is that without
something, psychic powers become largely exempt from the Reaction system, exacerbating the fact they're already fairly formidable in IRE.
I may need to fine tune the balance (it occurs that "half willpower" may be better than -20, so that high Wp characters don't have a really easy time of it, but it's also not impossible for low Wp characters to resist).
Short of completely redressing the balance of psychic power difficulties in IRE (and therefore causing back compatibility issues with the original rules) or slapping a broad -20 penalty across all psychic powers, it's proving quite a challenge to have hit the mid-ground where psykers aren't penalised for even thinking about using their powers but where they aren't completely overpowered gods.
For demonic possession Wp -30 is too high for the recovery test.
Possssssibly, but the problem for me is that almost all of the rare few times I've seen daemonic possession occur in a game it usually goes...
1) Daemon possesses character.
2) Daemon gets one or two actions of moving into position to try to do some damage
3) Daemon gets expelled at the start of the next turn
4) Character drops the daemon weapon.
... which isn't exactly thrilling.
Maybe things will be a bit different with IRE making possession both a bit more likely and less predictable (between Perils and the adjusted daemon weapons, it's now a case that it can happen at any time rather than just when the character already has reduced Wp, so avoiding it isn't just a case of dropping a daemon weapon), but I would like to see it as a bit more of a threat, where other characters actually have time to worry about it before it's over.
Possibly it should be -20 rather than -30, but I do think the roll should be
somewhat penalised so that it's not always completely transient.
Psychic nulls look interesting. Not completely effective but pretty nasty.
It's experimental right now, but they did need a large overhaul to bring them into line with the updated psychic rules having split psychic prowess into both Psy Rating and Willpower.