Before i go into the discussion of why it would work or not. I'd just like to say that its worth a visit to the PBE. I think we can learn a lot from the result and get a lot of insights out of the conversation that comes out of it.
regarding: assigning each individual a value...
agreed.mainly brainstorming there. theoretically ya you would have to. which is kind of the case with base ad though just less so and base ad plays a much bigger role in that it works with each auto attacks.
Another idea would be to add an If condition, where it won't scale as well if the player has more than such and such combined ad/crit chance. Again brainstorming.
but i still think its fine even if lichbane is stronger early. sure you could build it for funsies on an adc. but people will call you out for trolling. its doable but not optimal.
You are spending a lot of gold to get that damage.. why should lichbane be relegated to a 30 minute point in the game. so what if its ap. At the end of the day be it ad or ap its still just plain old damage. The only real difference is how you go about getting armor or magic penetration and whether or not you prefer to sustain from it.
Triforce still gives more base stats and the phage passive, this is enough to warrant the extra 700g cost even if both trigger about the same amount of damage from their sheen procs.
I think at least lich bane is in between triforce and ibg. Rylais/mallet and IBG are in an area of their own since slow items are designed to offer less stats given the potential usefulness of their slows, so naturally ibg's dmg ought to be toned down.
i mean think about it why am i getting less damage on an ap item without a slow field out of the gate compared to IBG. kind of a stretch but It'd be like luden's echo doing less damage than rylais out of the gate.
imo IBG could be around 2600 gold see post here
since you paying for 500 mana. It almost more of a mana item than a damage item.
So price wise it pretty much sits in between both. lich bane's sheen proc was designed to stand up to trinity force and/or even surpass. From the wikia: "The proc from Lich Bane item.png Lich Bane far surpasses Trinity Force item.png Trinity Force with a Rabadon's Deathcap item.png Rabadon's Deathcap alone on the majority of champions, not to mention other AP items."
Whereas triforces surpasses lichbane in terms of attackspeedcrit/sustain/utility.
what if you were a champion eyeing lichbane thinking you are being deprived of what otherwise could be a really cool item. Id be telling other champs something like. oh ya well i could stand up to you if items synergized with my kit as well as yours.
whats nice about my suggestion is that it gives lichbane two possible playstyles without either compromising the other. Full glass canon champions looking for that assassination potential will be unaffected. And can be used on champions who want to get as many sheen procs off over drawn out fights. Like phoenix udyr with rageblade and lichbane (what phoenix udyr's kit's been begging for) add righteous glory for mobility and now you have true diversity.
Hybrid champions have been neglected. This meet their needs.
Example, Ap bruiser evelyn. wota lichbane ap jungle item the rest tanky. or cinderhulk lichbane rylais.