Volcanic orb has has a 4 second cooldown even with the max node for increased cooldown recovery + additional global cooldown recovery you cannot get it below 0.7, 0.8 cooldown so basically it cannot be spammed.
In addition sorcerer damage is not at such a good spot to become OP IMO. I am now lvl 76 playing the frozen orb(cold) - volcanic orb build and still feels like damage is just fine, itemization is very poor. No much uniques to support sorcerer builds(except ignite/fire builds). So at this stage implementing a way to increase base mana regen will not be OP in any way with the volcanic orb build especially . On the contrary it may actually improve the sorcerer gameplay and not force you nearly always to skill focus in order to maintain your mana.