How about Health/Mana/Hybrid flasks only? Solve mana and life recovery at the expense of utility buffs. Trading for some wiggle room on tree/gear/auras. They could even flip it to "non-magic", since most of the mods are based around on-use they do little to nothing. Otherwise the instant recovery ones could be confusing/broken, making it non-magic also opens up unique flask options.

Divination Distillate, Replica Lavianga's Spirit, both strong but not broken. Zerphi's opens up some potential recovery if you can keep up with mana costs. Regular Lavianga's = free skills. Blood of the Karui, Doedre's, and Writhing Jar wouldn't do anything. Unless they wanted to hardcode them as full life recovered every 3 seconds, +1-3 minimum charges each, and permanent (cosmetic) worm pets.