Path of Exile Dev Tracker

Broadly yes. It wouldn't be able to be about number of withered debuffs, as individual debuffs can have modified effects, but it could e.g. make Withered have 100% increased effect on enemies poisoned by you, or similar.

You're tearing me apart, /u/_eLight_!

This is a technical limitation of how we're able to detect the condition and apply the bonus - it's applied as a conditional damage stat, which fundamentally are a part of hit calculation, so can only apply to hits (and damaging ailments, which are part of a hit and calculated with it). I came up with a potential long-term plan for a new system that would allow the keystone to be implemented in a different way that could apply to all damage, but it's complicated and wasn't feasible for this patch. It's something I'd like to do eventually, as I think that system would unlock some other potentially cool stuff, but at this point isn't even a complete plan, so not something to expect anytime soon.

c), but order is not random (in some cases it is arbitrary, but it's never random). Each hit is processed separately, and that includes stuff you do for blocking it if that hit was blocked. There is no "grouping" of hits - each is separate and sequential.

No.

"basing the dot off the actual damage dealt" only makes sense for ailments, and leads to double-dipping. Ignoring resistances for DoT would be a minor efficiency gain at best - there's still a bunch of other calculations that have to happen for damage taken, this is only removing a single step from a multi-step process (resistances, modifiers to type of damage taken as, modifiers to damage taken, modifiers to where damage is taken from, etc), and would lead to obviously wrong interactions - if you're taking fire damage, and do something that raises your fire resistance, that's obviously supposed to work, but wouldn't be able to under that system.

Doing that would be mechanically possible*, but prohibitively complicated and potentially a maintenance nightmare, because there is no unified code path that all sources of damage over time go through that this could be put into - different damage over time effects are applied in different ways so skills can do different things.

Individual DoT skills could easily apply such a resistance-penalising effect to things affected by their specific DoT effect, but making it generic to all skills would be harder (but still possible).

*with some finagling of wording - it would only be able to depend on them having the DoT on them, not being affected by it or actually taking the damage

Yes. That is the same thing.

Fundamentally, damage-over-time is calculated by the source only as a value of pre-mitigation damage-per-second to try to deal. That is applied to the target, which adds to a total value for damage per second they're taking of that type, and all mitigation and damage taking happens to the total, not to individual sources. Nothing about the source of a specific effect can do anything other than change the calculation of that initial, pre-mitigation dps value. Resistances are mitigation, so apply on the defender side to all damage-over-time of the appropriate type - different sources of damage over time can't be resisted differently, because this process isn't done to and has no concept of individual sources.

No, only the specific skill you dealt the crit with gets the benefit, not other skills with the same name.

This is not a "simple change". This fundamentally cannot happen without completely rewriting everything to do with taking damage over time from the ground up to be massively less efficient.