"Mind Drinker" passive, but for spells

I sometimes find, compared to the physical builds that I've made, that sustaining mana without using an Eldritch battery setup, is sometimes annoyingly difficult for most of my caster builds.

In the physical builds I've made, I usually end up taking mind drinker, which often solves most of my mana concerns, or at least helps mitigate the problem.

I'd like to see a caster variant on the tree. Whether it's elemental leech or spell leech.

Two cents.