Hawk Diesel
Adventurer
That's beyond the scope of this thread.
Well yes. So how would you balance it?
Sorry, but changes to the rules are typically done for a reason, and usually done to solve some perceived problem. Without knowing the reason for creating this rule, we can't adequately evaluate its viability because we have no criteria to judge it by.
Balance is a subjective thing, and so if we don't know how you define balance or what your purpose for this rule change is, it cripples the community's ability to provide the kind of feedback you seem to be seeking.
For example, this rule will absolutely make spellcasters that are not warlocks more powerful. But we also don't know if you perceive spellcasters to be weaker than non-spellcasters, or if you want some counterbalance to include in non-caster classes to merit inclusion of this rule. There's too much that we need to make assumptions about because we don't know the problem you are addressing, how you see this improving the game, or your ultimate goal regarding this rule. Without this information, we must use our own bias or perspective on how we play or use the game, which could be vastly different to how you play or use the game.
Thus if we are starting from widely differing playstyles, we have no common ground to determine if your suggestion has viability or utility for introduction into the game.