Rune Idea for benefiting "Manaless Champs"

This post is a consolidation and extension of comments I made on the linked Reddit post about the Transcendence Rune and stacking Black Cleaver build that evolved into it's own thing.

RIOT - hopefully one of you see's this because although it's not an issue when the enemy builds it. It becomes an issue when your own team builds it. So - I propose a fix, provide us a rune (or stat for currently existing rune) that converts Mana to AD/AP. In that way, those champions that require no Mana can also benefit from Mana inclusive items.

Items that also provide CDR but carry Mana stats like Iceborn Gaunlet, Frozen Heart, Triforce, are all great items but are never really picked up for Champions like Riven, Akali, Zed, Garen, Kennen, Lee Sin, Shen, Gnar, etc. The Mana stat is wasted on champions like this and so you end up with Quadruple Black Cleaver builds for the extra CDR.

Maybe I am just dreaming, maybe I complain too much, whatever - but think about it. The new rune or rune stat does not have to be in the same Sorcery tree as Transcendence. We could add it to the Domination tree (who uses Ghost Poro, amirite?). Or on the Precision tree, it would be great 2nd effect (maybe manaless champs exclusive) on Presence of Mind rune.

We can incorporate a somewhat level playing field by adjusting those benefits for "Mana champs" so it isn't OP. Like they did with Duskblade and Black Cleaver on ranged champs. So like +5 AD/AP (adaptive) for every 100 Mana. And +2.5 AD/AP for Champions that can use Mana. We can add it so that this benefit only comes from Items, or not, whatever those Riot Gods want to do.

TLDR: Include rune/rune stat for converting Mana to AD/AP so we can stop this stacking Black Cleaver nonsense.