Good questions.
First, I am most interested in the type of damage - passive, weapon or spell. There are a couple cases where I would use a tool to make sure I had no sources of passive damage, but usually I want as much passive damage as possible. Most of the time I want passive damage, other sources are capped so I would be maxing passive with weapon or spell up to some cap.
If I cared about damage types I'd be okay with another keyword. passive, prismatic.
I'd be OK with either using first round damage only, or coming up with some kind of damage over time calculation. I'm thinking maybe compute the average damage per round, over the first ten rounds? This also works with something that has a % to act. (Expected number of acts in ten rounds multiplied by the expected damage per act).
I wonder if treating this similar to clownosity or surgeonosity might work? Only consider equipment/items/effects that have the isPassive flag set.
I also wonder how often there will be multiple options for the same slot? There are five accessories, one back item, six offhand items and two pants. The pants only differ in whether the damage is sleaze or stench. The accessories can be ranked by damage since only one has an element and that is not player choose-able, I believe.
I don't think care for stinging damage as something the Maximizer knows about.