Dark already has an opposite, it's called Fighting.
Since when was Fighting the opposite of Dark? How the hell does that even work? Fighting's the "counterpart" to Psychic, the most Physical as Psychic's the most Special. Dark's the counterbalance to Psychic... meaning Dark and Fighting are on the same side.
That is some good logic you have there (seriously)
I really just want the Fire starter to end up being something other than pure fire (Typhlosion except based on another animal) or fire/fighting (Blaziken except not a chicken or a monkey)at it's final form.
About that Fire Psychic thing, that would probably end up being amazingly overpowered.
I still have yet to understand how most type weaknesses even work, such as Fighting > Dark and Bug > Dark