I think Mana Potions will be bring more option to custom specific Builds. For example Spellblade Shatter Strike always need Mana Strike from start to endgame and further playing that it’s so annoying. Mana Strike and other ways to generete mana should stay and using in campaign and mid game, but we could playing on endgame without that yet. Currently on some Builds I feel like I was playing d4, cast - generation - cast, it’s bad.
Technically we kinda already have mana potions, there is the Experimental affix on belts that can give upto 35 mana on potion use and there are two unique belts that give additional mana on potion use: Orian’s Descent and Harbinger of Stars (although harbinger gives mana based on how many meteors you have cast recently).
From personal experience no amount of mana potions will be enough for Shatterstrike as that skill needs to be spammed for its full damage. You can however scale enough mana/mana regen to kill stuff while clearing without using mana strike(and only use mana strike while spamming Shatterstrike on bosses). I remember seeing a build using Shatter strike with World splitter that did something like that.