WowAce

What is the enhancement in mind? How should it look and feel?
If you're trying to go for the Thaddius achievement, then a single charge is a "failure".  The current implementation of libfail allows for 3 charge spell damage before firing the notifications.  It would be nice to put this decision/policy into the clients.  Let my code decide whether my raid mates have failed.

For now, I'm just modifying my copy to fire the callbacks at the first charge spell damage.

you're right.

Thinking some more - there needs to be some consistency about what gets reported as a "fail" - otherwise people will wonder why they get different counts.

Any thoughts on how to implement this?

You could implement a function to set the min count for a special fail event (eg. LibFail:SetMinCount("Fail_Thaddius_PolarityShift", 1) )

so we have some constants in libfail for these kind of things, but the problem is they are global
so, ensidiafails right now customizes the built in thresholds ( libfail.THADDIUS_THRESHOLD = 8000 ) and that will affect every other mod using libfail too
now that might be both a good and a bad thing
the other solution might be to brake up the fail logic into different parts, one part that
"detects the possible fail" with maybe some low caps on it for when a fail would trigger on every spellcast or something
the higher up part would be near the fail event dispatch logic where you would check if its a fail or not, that could give us the flexibility needed, maybe even have a user callback to check if the target is a tank or not or something like that