What was stirring this up initially was my reading of the Razor Sharp quality.

Razor Sharp doubles the Pen ("of the hit") whenever you hit with 3+ DoS. Sounds nice, initially, but wait.

DoS are also used for things like Swift Attack or Full-Auto burst. Does that mean that whenever an attack that is able to cause multiple hits via DoS pays off, it also comes with doubled pen if performed with a Razor Sharp weapon? God I hope it isn´t so (though I don´t see much of another way). Because that would speak of really bad mechanics. Two totally unrelated things using the same cogwheel at the same time......

As of now I´d rule that only the hits that where really made with 3+ Dos (so for Instance the 3rd+ Full-Auto hit, or 2nd+ Semi-Auto hit) really benefit from the double Pen. Or is it just the initial hits? As in the other hits are just that, additional hits but they´re not "The Hit". Or is it really worst case?

This leads to other questions. Attacks that can score multiple hits and things that can occure once per attack.

Zealous hatred. Once per attack or once per hit?

Swapping a damage die result for DoS. Once per attack or once per hit?

I find it to be quite confusing.

If you swift attack with 3 DoS both hits get double pen. You can houserule this if you don't like it, the rule is easily vague enough to include both variations.

ZH happens every time you get a nat 10 on a damage roll. So any hit.

Swapping a damage die result for DoS. Once per attack or once per hit?

The die-swapping is explicitly noted to occur once per attack roll.